Charge-transporting thin film

ABSTRACT

This invention addresses the problem of providing a charge-transporting thin film with small variations in properties due to disturbance and small variations in resistance over time during application of current. The invention further provides a charge-transporting thin film with a secondary effect of small variations over time and stable luminescent properties. The charge-transporting thin film of the present invention contains one or more types of functional organic compounds having chiral elements, and is characterized in that the total of the number of chiral elements per molecule in each type of the functional organic compounds summed over all types of the functional organic compounds is four or more.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a 371 of PCT/JP2014/063454 filed on May 21, 2014,which, in turn, claimed the priority of Japanese Patent Application No.JP2013-107558 filed on May 22, 2013, both applications are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a charge-transporting thin film whichhas high stability.

BACKGROUND ART

Electronic devices to which an electric field is applied, such asorganic electroluminescent elements (hereinafter, also referred to as“organic EL elements”), solar cells, and organic transistors, generallyinclude charge-transporting thin films containing organic materialscapable of transporting charge carriers (generic terms includingelectrons and holes) during application of electric fields. Variousproperties are required for functional organic materials contained incharge-transporting thin films, and such functional organic materialshave been extensively developed in recent years.

Industrial components made of organic materials, particularly electronicdevices and electronic components to which a high electric field isapplied, generally involve problems due to the nature of the organicmaterials used therein, i.e. thermal degradation and electrochemicaldeterioration that are characteristics of organic substances. Most oftechnical improvements have been directed to enhance the robustness ofsuch organic materials per se. For example, organic materials, such ascopper phthalocyanine complexes, have been traditionally used inindustrial applications. They are dyes, but have characteristics likethose of pigments; they have a rigid chemical structure which rendersthem insoluble to any solvent, unlike other organic materials. The useof such organic materials unfortunately fails to exploit propertiescommon organic materials have, such as solubility, flexibility, chemicalreactivity, and compatibility with other materials. Such characteristicsof organic materials are inappropriate for future industrialapplications.

Organic materials are barely used in the form of a single isolatedmolecule in usual cases. They are often present in the form of anaggregate composed of a single type or different types of molecules(including different materials, such as metals or inorganic substances).

Meanwhile, molecular design has been essentially based on data of anisolated single molecule, typically data of structural analysis by X-raydiffractometry and molecular orbital calculation. In the actualcircumstances, the way of molecular design has not been very active inview of the coexistence of multiple molecules. A technique has beentherefore desired which focuses on the aggregates formed of molecules,to improve the stability of the aggregates at macroscopic level.

If no change occurs in a film or an article containing an organicmaterial during preservation or use, its properties should not change inany way. Properties required for such a film or article may varydepending on its application field. Examples of the required propertiesinclude a specific color, charge transfer properties, and opticalproperties such as a specific refractive index. In any case, if the filmor the article experience no change in its condition, its propertiesshould not change in any way, that is, it should have infinitedurability.

For example, charge-transporting thin films require continuousapplication of an electric field during use. Thus, they should havesufficient durability over time during application of current. Inparticular, they should not show unfavorable variations in chargetransfer characteristics, i.e. variations in resistance, in view oftheir intended purpose of use. A charge-transporting thin film istherefore desired which shows a small change in resistance during theapplication of current.

Disclosed conventional techniques of improving the stability of the thinfilm rely on use of various compounds alone or in combination. Forexample, PTL 1 discloses a metal complex having a specific ligand as ablue phosphorescent compound. Some reports also disclose that combineduse of two dopants which emit light of similar colors provide a devicewith higher efficiency, a prolonged lifetime, and a lower drivingvoltage (see, for example, PTLs 2, 3 and 4).

Unfortunately, even such techniques fail to achieve sufficient stabilityrequired for charge-transporting thin films, where a current isgenerally applied for a long time, under conditions expected in themarket. There has been therefore need for a radical solution to such aproblem.

RELATED ART DOCUMENTS Patent Documents

PTL 1: U. S. Patent Application Publication No. 2011/0057559

PTL 2: Japanese Patent Application Laid-Open Publication No. 2008-112976

PTL 3: Japanese Patent No. 4110160

PTL 4: U.S. Pat. No. 7,807,992

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

An object of the invention, which has been accomplished under suchcircumstances, is to provide a charge-transporting thin film with smallvariations in properties due to disturbance and small variations inresistance over time during application of current. The inventionfurther provides a charge-transporting thin film with a secondary effectof small variations over time and stable luminescent properties.

Means for Solving the Problems

The inventors have been studying the source and solution of the problemsdescribed above, and have consequently reached the following findings.The extent of a variation in film characteristics due to disturbance,i.e. the stability of the film, can be expressed by the magnitude of theGibbs free energy change (ΔG) in the film, from a thermodynamicperspective. The more negative the value of ΔG is, the higher stabilitythe film has. The value of ΔG is represented by the expression below. Inthe present invention, the inventors have intended to accomplish theobject of the invention by actively exploiting effects of entropy change(ΔS) as a measure to achieve a more negative value of ΔG.ΔG=ΔH−TΔS

The inventors have made extensive studies based on the idea of activelyexploiting ΔS, and have consequently found that use of functionalorganic compound(s) having chiral elements can increase the value of ΔS,resulting in a significant increase in stability of the film, withoutsubstantial changes in physicochemical properties of the film. Based onsuch findings, the inventors have completed the present invention.

The present invention involves the following aspects:

1. A charge-transporting thin film containing one or more types offunctional organic compounds having chiral elements, wherein the totalof the number of chiral elements per molecule in each type of thefunctional organic compounds summed over all types of the functionalorganic compounds is four or more.2. The charge-transporting thin film according to item 1, wherein thetotal of the number of chiral elements per molecule summed over alltypes of the functional organic compounds is within a range of five tofifteen.3. The charge-transporting thin film according to item 1 or 2, whereinthe charge-transporting thin film comprises at least two types of thefunctional organic compounds having chiral elements, and each of the atleast two types of the functional organic compounds includes at leastone isomer selected from enantiomers and diastereomers.4. The charge-transporting thin film according to any one of items 1 to3, wherein the charge-transporting thin film comprises at least twotypes of the functional organic compounds having chiral elements, atleast one of the functional organic compounds includes both enantiomersand diastereomers.5. The charge-transporting thin film according to any one of items 1 to4, wherein

the charge-transporting thin film comprises at least two types of thefunctional organic compounds having chiral elements, at least one of thefunctional organic compounds is a metal complex; and

the metal complex has two or more chiral elements per molecule, andthereby includes both enantiomers and diastereomers.

6. The charge-transporting thin film according to any one of items 1 to5, wherein the charge-transporting thin film comprises at least twotypes of the functional organic compounds having chiral elements, all ofthe at least two types of the functional organic compounds includes bothenantiomers and diastereomers.7. The charge-transporting thin film according to any one of items 1 to6, wherein the functional organic compounds having chiral elements havea biaryl structure which has chiral elements due to hindered rotationbetween two aryl moieties, such that the functional organic compoundsinclude an atropisomer.8. The charge-transporting thin film according to any one of items 1 to7, wherein the at least one type of the functional organic compoundshaving chiral elements is a compound which emits light during excitationunder an electric field.9. The charge-transporting thin film according to item 8, wherein thecompound which emits light during excitation under an electric field isthe metal complex.10. The charge-transporting thin film according to any one of items 1 to9, wherein

the charge-transporting thin film contains the functional organiccompounds having chiral elements; and

a volatile organic material having a boiling point lower than 300° C.under normal pressure, wherein the volatile organic material has anasymmetric carbon atom.

11. The charge-transporting thin film according to any one of items 1 to10, wherein

each of the functional organic compounds contained in thecharge-transporting thin film comprises a mixture of the enantiomers anddiastereomers;

the charge-transporting thin film contains a volatile organic materialhaving a boiling point lower than 300° C. under normal pressure; and

the volatile organic material has an asymmetric carbon atom.

Advantageous Effects of the Invention

The present invention provides a charge-transporting thin film withsmall variations in properties due to disturbance and small variationsin resistance over time during application of current. The inventionfurther provides a charge-transporting thin film with a secondary effectof small variations over time and stable luminescent properties.

The mechanism of the advantageous effect of the present invention ispresumed as described below.

The present invention effectively exploits entropic effects offunctional organic compound(s) having chiral elements. Unlikeconventional techniques, the configuration of the inventionintentionally employs a configuration with a combination of functionalorganic compounds such that intended effects are achieved at a very highlevel.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic view illustrating entropy change in mixing of twogases.

FIG. 1B is a schematic view illustrating entropy change in mixing of twogases.

FIG. 2A shows an example of color image fastness achieved with a chelatecomplex dye.

FIG. 2B shows an example of color image fastness achieved with a chelatecomplex dye.

FIG. 3A is a schematic view illustrating a change in state of a chargetransport layer or a transporting thin film.

FIG. 3B is a schematic view illustrating a change in state of a chargetransport layer or a transporting thin film.

FIG. 4A is another schematic view illustrating a change in state of acharge transport layer or a transporting thin film.

FIG. 4B is another schematic view illustrating a change in state of acharge transport layer or a transporting thin film.

FIG. 5A is a schematic view illustrating hopping transfer andrecombination in charge transfer.

FIG. 5B is a schematic view illustrating hopping transfer andrecombination in charge transfer.

FIG. 6 is a schematic view of HOMO and LUMO energy levels of theindividual molecules A₁ to A₄.

FIG. 7 is a schematic view illustrating a charge recombination thin filmcomposed of five types of molecules.

FIG. 8A is a view illustrating an exemplary structure of an organicthin-film transistor.

FIG. 8B is a view illustrating another exemplary structure of an organicthin-film transistor.

FIG. 8C is a view illustrating another exemplary structure of an organicthin-film transistor.

FIG. 8D is a view illustrating another exemplary structure of an organicthin-film transistor.

FIG. 8E is a view illustrating another exemplary structure of an organicthin-film transistor.

FIG. 8F is a view illustrating another exemplary structure of an organicthin-film transistor.

FIG. 9 shows an example of schematic equivalent circuit diagram oforganic thin-film transistors.

FIG. 10 shows an example of an M-plot of organic EL devices withdifferent thicknesses of the electron transport layer.

FIG. 11 shows an example relation between the thickness and theresistance of the layer.

FIG. 12 shows an exemplary equivalent circuit model of the organicelectroluminescent element.

FIG. 13 shows example analytical results indicating the relation betweenthe resistance and the voltage for each layer.

FIG. 14 shows example analytical results of organic EL devices afterdeterioration.

FIG. 15 is a diagrammatic view of a lighting device.

FIG. 16 is a cross-sectional view of the lighting device.

FIG. 17A is a diagrammatic view illustrating a structure of an organicEL full-color display device.

FIG. 17B is a diagrammatic view illustrating a structure of an organicEL full-color display device.

FIG. 17C is a diagrammatic view illustrating a structure of the organicEL full-color display device.

FIG. 17D is a diagrammatic view illustrating a structure of the organicEL full-color display device.

FIG. 17E is a diagrammatic view illustrating a structure of the organicEL full-color display device.

FIG. 18 is a partial cross-sectional view illustrating an exemplarystructure of a photoelectric device.

FIG. 19 illustrates delta and lambda isomers of octahedral complexescoordinated with bidentate ligands.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The present invention provides a charge-transporting thin filmcontaining one or more types of functional organic compounds havingchiral elements, wherein the total of the number of chiral elements permolecule in each type of the functional organic compounds, when summedover all types of the functional organic compounds, is four or more.These technical features are commonly owned by the inventions accordingto claims 1 to 11.

In an embodiment of the present invention, the total of the number ofchiral elements per molecule summed over all types of the functionalorganic compounds is preferably within a range of five to fifteen, fromthe viewpoint of the advantageous effects of the present invention. Theelectronic device of the invention preferably contains at least twotypes of the functional organic compounds having chiral elements, andeach of the at least two types of the functional organic compoundsincludes at least one isomer selected from enantiomers anddiastereomers. The electronic device of the invention preferablycontains at least two types of the functional organic compounds havingchiral elements, and at least one of the functional organic compoundsincludes both enantiomers and diastereomers.

The electronic device of the invention preferably contains at least twotypes of the functional organic compounds having chiral elements, and atleast one of the functional organic compounds is a metal complex; andthe metal complex preferably has two or more chiral elements permolecule, and thereby includes both enantiomers and diastereomers.

According to the present invention, the electronic device preferablycontains at least two types of the functional organic compounds havingchiral elements, and all of the at least two types of the functionalorganic compounds include both enantiomers and diastereomers.

The functional organic compounds preferably have a biaryl structurewhich has chiral elements due to hindered rotation between two arylmoieties, such that the functional organic compounds include anatropisomer.

At least one type of the functional organic compounds having chiralelements is preferably a compound which emits light during excitationunder an electric field. The compound which emits light duringexcitation under an electric field is preferably the metal complex.

The charge-transporting thin film of the electronic device of theinvention preferably contains the one or more types of functionalorganic compounds having chiral elements; and a volatile organicmaterial having a boiling point lower than 300° C. under normalpressure, wherein the volatile organic material has an asymmetric carbonatom. Each of the functional organic compounds contained in thecharge-transporting thin film includes a mixture of the enantiomers anddiastereomers. The charge-transporting thin film preferably furthercontains a volatile organic material having a boiling point lower than300° C. under normal pressure. The volatile organic material preferablyhas an asymmetric carbon atom.

The charge-transporting thin film of the present invention may beappropriately included in an electronic device, an organicelectroluminescent element, an electrically conductive film, an organicthin-film solar cell, and a dye-sensitized solar cell.

The elements and embodiments of the present invention will now bedescribed in detail. As used herein, the expression “to” indicating anumerical range is meant to be inclusive of the boundary values.

Before getting to the body of the description, the thermodynamicbackground on the technical idea of the present invention will bedescribed.

[Thermodynamic Background]

One of the industrial products primarily composed of organic materialsis a color photographic material. In particular, color papers (colorphotographic paper) are to be visually enjoyed; hence, an importanttechnical element for the color image is high stability over time(referred to as preservability).

Color paper, for example, contains an ultraviolet absorber for thepurpose of preventing light fading in color photographic images.Hydroxyphenylbenzotriazole derivatives are typical ultravioletabsorbers, and two or more of the derivatives are frequently present incolor paper in the form of a mixture, for several reasons. For example,prevention of crystallization during long-term preservation is afundamental requirement for ultraviolet absorbers and a mixture ofseveral hydroxyphenylbenzotriazole derivatives effectively can inhibitcrystallization for practical use. This phenomenon will be now discussedfrom thermodynamic viewpoints.

If no change occurs in a film or an article containing an organicmaterial during preservation or use, its properties should not vary inany way. Characteristics required for such a film or article may varydepending on its application field. Examples of the requiredcharacteristics include development of colors, charge transfercharacteristics, and optical characteristics such as a specificrefractive index. In any case, if the film or the article experience nochange in its condition, its characteristics should not vary in any way,that is, it should have infinite durability.

The stability of a film or an article (hereinafter, merely referred toas “film” for simpler explanation) depends on a change in Gibbs freeenergy (ΔG) as defined in the second law of thermodynamics.Specifically, a film having a more negative value of ΔG has higherstability and thus barely undergoes variations in characteristics due todisturbance in use. The value of ΔG is represented by the followingexpression involving enthalpy change (ΔH) and the product of entropychange and temperature (TΔS):ΔG=ΔH−TΔS

The essence of the technique of the present invention lies in effectiveexploitation of entropic effects as a measure to achieve a more negativevalue of ΔG to increase the stability of a formed film, whichconsequently achieves smaller variations in characteristics of the film.

The concept of entropy will be now explained.

In general, all gases are completely miscible with other gases. Almostall types of gas molecules are miscible with each other homogeneously,for the reason explained below with reference to FIG. 1A and FIG. 1B.FIG. 1A and FIG. 1B are schematic views illustrating entropy change inmixing of two gases.

It is supposed that a box divided by a partition in the central portioncontains nitrogen molecules (component A) and oxygen molecules(component B) at the same packing density in the respective sections ofthe box (see FIG. 1A, left). When the partition is removed, the oxygenmolecules and the nitrogen molecules mix with each other completely (seeFIG. 1A, right). Since they are both gases, it is believed that theenthalpy does not substantially decrease. When the partition is removed,for example, the degree of disorder of the nitrogen molecules increasesdue to the coexistence of different molecules, i.e., the oxygenmolecules, as compared to that before the removal. Such disorder meansan increase in entropy. Unless the absolute temperature is zero (0K(Kelvin)), the value of TΔS is positive, and thus the value of ΔG isnegative. In other words, the entropic effect contributes to homogeneousmixing of gases.

Another case is supposed where both sections of the box contain nitrogenmolecules (component A) at the same packing density (i.e. the samenumber of molecules). In such a case, the removal of the partition (seeFIG. 1B, right) does not result in increase in the number of differentmolecules for the nitrogen molecules or change in the packing density ofthe nitrogen molecules, as compared to those before the removal (seeFIG. 1B, left). Thus, no entropy change occurs. In other words, thecoexistence of different molecules is essential for exertion of entropiceffects.

This principle is applied to ultraviolet absorbers.

A benzotriazole derivative having tert-amyl substituent group isreferred to as BT-1 (component A), and another benzotriazole derivativehaving tert-butyl substituent group is referred to as BT-2 (componentA).

The schematic view shown in FIG. 1A corresponds to combined use of BT-1and BT-2 and that shown in FIG. 1B corresponds to use of BT-2 alone, infilm formation.

It can be understood that the Gibbs free energy of the resulting filmhas a more negative value, that is, the film is more stable, in thecombined use of BT-1 and BT-2 (corresponding to FIG. 1A) than in thesingle use of BT-2 (corresponding to FIG. 1B), as in the case of mixingof nitrogen and oxygen. Since BT-1 and BT-2 have a common basicstructure, hydroxyphenylbenzotriazole, which is involved in theinteraction, it is believed that they have substantially identicalenthalpy values. This effect of improving stability is due to theentropic effect caused by the coexistence of different molecules. Inother words, in use of a mixture of ultraviolet absorbers BT-1 and BT-2,it is believed that the entropic effect contributes to the effect ofpreventing crystallization of ultraviolet absorbers during long-termuse. Very few evidences have been reported which demonstrate or discusssuch prevention of crystallization from thermodynamic viewpoints.Entropy (degree of disorder) is more difficult to imagine in a realsituation than enthalpy (attractive force). Due to such difficulty, mostevidences do not discuss a technique of improving durability by activeexploitation of entropy regardless of its significant effect.

The most representative examples of exploitation of entropic effects forstability are metal complexes. Table 1 shows thermodynamic parametersfor various amine complexes of cadmium, as calculated based on thestability of each complex measured at a room temperature.

TABLE 1 log β −ΔG⁰ −ΔH⁰ TΔS⁰ No. Complex compound (kJ/mol) (kJ/mol)(kJ/mol) (kJ/mol) 1 Cd(NH₂)₂ ²⁺ 4.95 28.2 29.8 −1.5 2 Cd(MeNH₂)₂ ²⁺ 4.8127.4 29.4 −1.9 3 Cd(H₂NC₂H₄NH₂) 5.84 33.3 29.4 3.9

For example, the complex No. 3 (cadmium-ethylenediamine complex) is achelate complex, while the complex No. 2 (cadmium-bismethylaminecomplex) is not a chelate complex. Comparison of these complexesindicates that they are the same in enthalpy (which may be interpretedas attractive force) but significantly differ in entropy. The differencein entropy, i.e. 5.8 kJ/mol, indicates the difference in stabilitybetween the chelate and non-chelate complexes. This value indicates asignificant stabilization energy corresponding to 21% of the Gibbs freeenergy of the complex No. 2.

The high stability of chelate complexes can be intuitively understood,and is generally and widely known. It, however, is not commonly knownthat entropic effects largely contribute to the significant energy. Thesource of the entropic effects will be now described. Entropy can alsobe represented by the product of Boltzmann constant and the number ofconstituent molecules. A change in the number of constituent moleculeshelps better understanding of entropic effects of chelate complexes.

Formula (a) shows that the number of constituent molecules in thenon-chelate complex No. 2 is three both before and after complexformation. Meanwhile, Formula (b) shows that the number of constituentmolecules in the chelate complex No. 3 is two before complex formationand increases to three after complex formation, which indicates anincrease in entropy.

The extent of influence of the chelate complex formation on thedurability of a resulting product will now be explained with a specificexample (see KONICA TECHNICAL REPORT, pp. 83-86, vol. 14 (2001)).

Konica Photo Chelate (registered trademark) is a print material forpost-chelating dye transfer print. In its image formation method, a dyehaving a structure as a ligand is transferred by diffusion onto an imagereceiving layer containing a metal ion compound, and then reacts withthe metal ion compound to form a chelate. A chelate dye is therebyproduced and fixed on the image receiving layer. The produced image dye(chelate complex dye) provides improved image fixation and light andheat resistances, which achieves excellent durability for printedimages.

The effect is demonstrated by comparing FIG. 2A and FIG. 2B. FIG. 2A andFIG. 2B respectively show examples of color image fastness achieved withindividual chelate complex dyes based on results of dark fading test ata temperature of 65° C., indicating variations in color density forcyan, magenta, and yellow dyes respectively represented by C, M, and Y.FIG. 2A shows the results of a test achieved in printing with KonicaPhoto Chelate using chelate complex dyes, and FIG. 2B shows thoseachieved in ordinary thermal dye transfer printing. The results areclearly distinct, and indicate that no fading occurs in the image dyesof Photo Chelate even under high-temperature preservation.

Specifically, in Photo Chelate, the entropy of the film containing dyesis greater at the time of image formation and the entropic effectprovides a stable film. As a result, the film satisfies industrialrequirements of image preservability.

Thus, by effectively exploiting the entropic effect, it is possible toprovide a film mainly composed of organic materials with increased Gibbsfree energy in the initial state. This effect of increasing Gibbs freeenergy is high enough to prevent variations in characteristics of thefilm even under severe environments, such as long-term orhigh-temperature preservation.

[Increase in Entropy in Charge-Transporting Thin Film]

The main subject of the present invention is a charge-transporting thinfilm. The concept of the invention will now be described with referenceto the drawings, focusing on a technique of increasing Gibbs free energyof the film, from the view point of charge transfer. FIG. 3A and FIG. 3Bare each a schematic view illustrating a change in state of a chargetransport layer or a thin transport film.

For example, a film is supposed which contains molecules A and B havingmutually different functions as shown in FIG. 3A, left, and whichundergoes changes in state of the molecules A and B as shown in FIG. 3A,right, after application of current or long-term preservation.

Other molecules A₁ and A₂ are supposed which have the same function asthe molecule A but are different from the molecule A in structure. Themolecules A₁ and A₂ are different molecules although they have the samefunction, and thus may be a factor to cause disorder, according to theconcept of entropy. In other words, the film containing a mixture ofthree components, i.e. the molecules A₁, A₂, and B, as shown on the leftin FIG. 3B has a higher degree of disorder, in comparison with the filmshown on the left in FIG. 3A. This indicates that the original Gibbsfree energy is more negative in the film shown on the left in FIG. 3Bthan in that shown on the left in FIG. 3A. Thus, even if the film shownin the schematic view of the left in FIG. 3B is exposed to the sameconditions where the film shown on the left in FIG. 3A undergoes achange as shown on the right in FIG. 3A, the change in state shown onthe right in FIG. 3B is smaller than that shown on the right in FIG. 3A.

This technical concept is expanded as shown on the left in FIG. 4A andthe left in FIG. 4B.

In FIG. 4A, left, molecules A consist of four mutually differentmolecules A₁, A₂, A₃ and A₄. In FIG. 4B, left, molecules B are alsoshown as two mutually different molecules B₁ and B₂. From the viewpointof entropy, such an increase in the number of components directlycontributes to an increase in entropy, so as to achieve a significanteffect on an improvement in stability.

Polymer materials are generally believed to have excellent film-formingproperties. In other words, the initially formed thin film is lesslikely to undergo variations in its characteristics over time.

Polymer materials are generally believed to have excellent film-formingproperties. In other words, the initially formed thin film is lesslikely to undergo variations in its characteristics over time.

Since a polymer composed of the same repeating units is believed to havesimilar enthalpy values corresponding to attractive force betweenmolecules, the excellent film forming properties of polymers areprobably due to the entropic effect.

Meanwhile, use of a polymer in a charge-transporting thin film as in thesubject of the present invention involves the following disadvantages:If the charge-transporting thin film is mainly composed of organicmolecules, most charge transfer occurs via intermolecular hopping. Insuch a case, trace amounts of impurities produce trap levels, whichhinders the charge transfer and thus impairs original properties of thepolymer. For this reason, when polymers are applied to organic ELdevices or organic thin-film solar cells, removal of such impurities isa major obstacle.

Radically polymerized polymers also involves a problem: the presence ofthe moiety from a radical initiator in the end of the resulting polymeris disadvantageous for a charge-transporting thin film to be applied toelectric field devices. In polymer synthesis involving a reaction suchas Suzuki coupling or Negishi coupling, use of a transition metalcatalyst is essential, and the residual catalyst frequently produce traplevels, which causes fatal defects. Thus, atoms and ions of thetransition metal must be perfectly removed to ppm levels, which is agreat limitation for such industrial application.

Polymers also have fatal defect that fine purification such asrecrystallization or sublimation cannot be applied, unlike low-molecularweight compounds.

Another disadvantage of polymers is that they do not have the samephysicochemical properties of their repeating units, and essentialphysical properties for a charge-transporting thin film, for exampleHOMO and LUMO levels, absorption spectrum, and emission spectrum, varydepending on their degree of polymerization and conformation, whichcauses a higher level of difficulty in active molecular design of apolymer molecule having a specific action of interest, as compared tomolecular design of a low-molecular weight compound composed of a singlemolecule.

If the advantage of polymers can be achieved with low-molecularcompounds while solving the disadvantages of polymers, thenlow-molecular weight compounds can be actively applied to both vapordeposition and wet deposition process, such as coating and ink jetting.If future electronic devices are required to have higher performances,use of such low-molecular weight compounds can combine the excellentfilm forming properties of polymers, i.e. higher stability of acharge-transporting thin film, with their characteristics oflow-molecular weight compounds, i.e. easy molecular design, easy finepurification, and easy achievement of major physical properties ofinterest, such as specific energy levels and spectra. Such low-molecularweight compounds are appropriate for future industrial applications.

It is an essential requirement for industrial developments to providesuch an ideal low-molecular weight material, and technologicalinnovation in the field of materials depends on achievement of such amaterial. In other words, it is no exaggeration to say that thetechnological innovation depends on achievement of a technique foractivation of entropic effect in a low-molecular weight material.

[Stability of Charge-Transporting Thin Film]

In the foregoing description, ideal low-molecular-weight materials arediscussed from the viewpoint of film stability. Meanwhile, since thepresent invention is applied to a charge-transporting thin film,materials used in the charge-transporting thin film have limitations asdescribed below. Organic materials are basically insulating materials,and thus charge transfer therein occurs via a phenomenon referred to ashopping.

Charge transfer via hopping is explained with reference to the drawings.FIG. 5A and FIG. 5B are schematic views illustrating hopping transferand recombination in charge transfer, respectively.

As shown in FIG. 5A, charge carriers (in FIG. 5A, electrons) areinjected from an electrode into organic material A, and transfer byhopping from a molecule A to an adjacent molecule A, and finally theelectrons are donated to the counter electrode to produce electroncurrent. A phenomenon referred to as charge recombination is anothertype of charge transfer based on the same principle. Regarding holes asempty molecules from which electrons have been ejected, donation ofelectrons to the counter electrode is synonymous to injection of holesfrom the counter electrode.

FIG. 5B schematically shows a model of charge recombination. In thismodel, electrons are injected from a cathode and holes are injected froman anode, and charges from the individual carriers recombine together onthe molecule B. If the molecule B is a luminescent substance, light isemitted when the excited molecule B returns to the ground state, thatis, an organic EL device is provided.

In charge transfer occurring in a thin film composed of organicmaterials, carrier trap should be taken into consideration.

FIG. 6 is a schematic view of HOMO (highest occupied molecular orbital)and LUMO (lowest unoccupied molecular orbital) energy levels of theindividual molecules A₁ to A₄ which have the same function as themolecule A. FIG. 7 is a schematic view illustrating a thin chargerecombination film composed of five types in total of molecules, i.e.molecules A₁ to A₄ having the same function as the molecule A andmolecule B having a different function.

In FIG. 6, the HOMO and LUMO energy levels shown at a lower portion ofthe figure is farther from the vacuum level (i.e. deeper level).Electrons injected from one of the electrodes do not enter all themolecules A₁ to A₄ at the same probability. They are always injected orlocalized at higher probability in molecules having deeper LUMO levels.When holes are injected from an anode, they are injected or localized athigher probability in a molecule having a shallower HOMO level.

For example, it is supposed that the molecules A₂ have a deeper LUMOlevel than the other three types of molecules and the molecules A₄ havea shallower HOMO level than the other three types of molecules. Ifelectric fields are applied to a thin film containing such molecules,electrons are trapped by the molecules A₂ at high probability and holesare trapped by the molecules A₄ at high probability, which consequentlydecreases the probability of intended recombination of the electrons andthe holes at the molecules B.

If the molecule B is a luminescent substance and the film shown in FIG.7 is used in an organic EL device, increased amounts of electrons andholes are required to generate a sufficient amount of excitons in themolecules B in order to achieve a specific luminance. Increases inamounts of carriers to be injected results in a higher driving voltage,and continuous application of high driving voltage increases amounts ofcarriers to be captured in carrier traps. Since energy of capturedcarriers is converted to vibrational energy that is not involved inemission of light, the additionally injected electrons and holeseventually waste their energy in the form of heat. The thin filmcontaining the molecules B is then locally heated to a high temperature,which results in higher tendency of changes in the state of the thinfilm. Therefore, a mere increase in the number of components does notwork, and it is essentially required to use in combination multipletypes of molecules which have a certain common function andsubstantially identical energy levels.

In this theory, some industrial issues should also be taken intoconsideration.

First, it is required to design multiple types of molecules havingsubstantially identical energy levels. Of course, the molecules shouldbe prepared in a sufficient amount and so as to satisfy thespecification, such as purity, required for practical use. If vacuumvapor deposition is employed in formation of a film, the required numberof vapor deposition sources corresponds to the number of components. Itis substantially impossible to prepare five or more vapor depositionsources in a single vacuum chamber, from the viewpoint of manufacturingcosts.

The essence of the present invention lies in a method to solve theseproblems simultaneously. A measure to solve the problems is to usefunctional organic compounds having chiral elements, which can increaseΔS, resulting in a significant increase in stability of the film,without substantial changes in physicochemical characteristics of thefilm. Preferably, functional organic compounds including at least oneisomer selected from enantiomers and diastereomers is used. Use ofmaterials composed of many different molecules having a common functioncauses the resulting charge-transporting thin film to have a morenegative Gibbs free energy at the initial state after the formation(i.e. the resulting thin film barely undergoes variations incharacteristics due to thermal, electric, or light disturbance). Asexplained above, this effect is caused by increased entropy, notdepending on a specific chemical structure, and thus can be exploited asa universal measure for improving the stability.

Enantiomers are defined as isomers that have identical physicochemicalproperties, except for physiological activity. Diastereomers are definedas isomers which do not have identical physicochemical properties likeenantiomers but have very similar physicochemical properties. Theenantiomers and diastereomers therefore do not substantially lead toundesired carrier traps explained with reference to FIG. 7.

At the time of purification to obtain a final product, enantiomers anddiastereomers are not completely separated as single materials, when apurification method without chiral sources is applied. Thus, use ofenantiomers and diastereomers is very reasonable to prepare a mixture ofa large number of different molecules by a single synthetic andpurification procedure.

<<Enantiomers and Diastereomers>>

Enantiomers and diastereomers will now be described in detail.

The compound shown above are major types of the organic functionalcompound having chiral elements according to the present invention.Formula (I) shows the most common type, a compound with an asymmetriccarbon atom, i.e. a compound having a carbon atom (or an atom havingunpaired electrons, such as nitrogen, sulfur, or phosphorus atom) whichhas four different substituent groups. Formula (II) shows an axiallychiral compound, i.e., a molecule which has a bulky substituent groupsat ortho positions of individual moieties such that the bond axisbetween the two moieties is rotationally hindered (atropisomeric axis),resulting in rotational isomerism of the molecule. An example of such astructure is a biaryl structure. Formula (III) shows a compound withplanar chirality, i.e., a compound having two aromatic rings which arefixed or cannot easily rotate, so as to cause chiral elements. Formula(IV) shows a helical compound having a predetermined direction of twist.An examples of such a compound is helicene. The organic functionalcompound of the present invention also include compounds which exhibitasymmetric mirror images by complex formation. FIG. 19 illustratesoctahedral complexes coordinated with bidentate ligands includeenantiomers, i.e. isomers which are mutually in mirror-imagerelationship, referred to as A (delta) and A (lambda) isomers(respectively corresponding to right-handed and left-handed propellers).

Enantiomers are also referred to as mirror-image isomers which are in amirror-image relationship like right and left hands. This applies notonly to compounds with an asymmetric carbon atom but also to thecompounds of Formulae (II), (III) and (IV), and other materials havingchiral elements. In any of these types, isomers in a mirror-imagerelationship are referred to as enantiomers, and in other words, theyare in an enantiomeric relationship to each other.

“Diastereomers” refers to molecules which arise if two or more chiralelements are present and which are not in a mirror-image relationshipbut appear identical based on two-dimensional representation of theirmolecular structure. In other words, the molecules are in adiastereomeric relationship.

A specific example of a compound having three asymmetric carbon atoms isas follows.

This molecule has eight isomers. Among them, four pairs of isomers areeach in a mirror-image relationship, that is, enantiomeric, and theother pairs are each diastereomeric. Double-headed solid arrowsrepresent an enantiomeric relationship, and double-headed dashed arrowsrepresent a diastereomeric relationship.

A specific example of a compound having one axial chirality and oneasymmetric carbon atom is shown below. Any types of chirality can becombined.

In complexes having multiple ligands, such as trivalent hexacoordinateiridium complexes, if one of their ligands has a chiral element, theresulting complex has multiple chiral elements. As a result, the complexnaturally includes diastereomers.

Even if a ligand itself does not have any chiral element or anypossibility of the presence thereof, complex formation may induce axialchirality, planar chirality, or helicity, and the resulting complex mayhave multiple chiral elements. Such complexes may also be used in thepresent invention.

The following point should be remembered.

Some documents, for example, Japanese Unexamined Patent ApplicationPublication No. 2008-525995 and Japanese Patent Application Laid-OpenPublication No. 2007-177252, disclose techniques of improving devicelifetime with isomeric compounds. Unfortunately, these techniques happento exploit entropic effects, and do not intentionally employ aconfiguration with a combination of compounds in order to achieveintended effects. Although the conventional techniques happen to providesome effects, the effects have been inadequate for general use inindustrial applications. Consequently, it would not have been easilyinferred from the conventional techniques which just happen to exploitentropic effects to apply the effect as a measure to solve the problemsto arrive at the solution to the problems provided by the presentinvention as will be described below. The solution to the problems hasbeen achieved by the present invention for the first time.

Many other documents disclose exemplary compounds without identifyingwhether they are enantiomers or diastereomers, although two-dimensionalrepresentation thereof implies possible presence of enantiomers ordiastereomers. Of course, some of the known compounds should contributeto high entropic effects when they are actively used in combination withat least one isomer selected from enantiomers and diastereomers for thefollowing reason: The essence of the technical idea of the presentinvention lies in “coexistence of different molecules having identicalenergy level”, basically regardless of the types (known or unknown) andmolecular weights and chemical structures of the compounds to be used.

In other words, even if some of the compounds disclosed in these knowndocuments incidentally contribute to the coexistence of multipleenantiomers or diastereomers, these known techniques should bedistinguished from the present invention, unless they clearly indicatethe intention to actively use such isomers to achieve a thin film withmore negative Gibbs free energy, or the intention to use a mixture ofisomers to achieve a film with increased entropy in the initial state.The inventors have carefully researched conventional documents, but havefound no disclosure of such a technical idea.

<<Charge-Transporting Thin Film>>

The charge-transporting thin film according to the present inventioncontains one or more types of functional organic compounds having chiralelements, wherein the total of the number of chiral elements permolecule in each type of the functional organic compounds, when summedover all types of the functional organic compounds, is four or more.

For example, ortho-metalated iridium complexes having a facialconfiguration with a hexadentate ligand have one chiral element instructure, and are known as materials for organic EL thin films.However, the advantageous effects of the present invention cannot beachieved with such complexes alone, and slight effects observed withcompounds having two or three chiral elements are still insufficient.Meanwhile, an increased number of chiral elements should increase theadvantageous effect of the present invention. This is probably because asmaller number of chiral elements renders the resulting thin film moresubject to influences by other factors.

As explained above, a greater total number of chiral elements ispreferred. The total number of chiral elements is preferably at leastfive, more preferably at least six, and further more preferably at leastseven. The total number of optically active elements has no particularupper limit, and a greater total number of chiral elements is morepreferable for achieving the advantageous effects of the presentinvention, because it enhances the entropic effects while havingsubstantially identical energy levels.

The term “charge-transporting thin film” (also referred to as “organicfunctional layer”) refers to a layer containing a functional organiccompound capable of transporting charge carriers (generic termsincluding electrons and holes) during application of electric fields.Such a charge-transporting thin film is applied to electronic devices,such as organic EL devices, organic thin-film solar cells,dye-sensitized solar cells, and organic thin-film transistors.

Examples of the charge-transporting thin film used in the presentinvention include a hole blocking layer, an electron blocking layer, anelectron injection layer, and a hole injection layer, in addition to ahole transport layer, a photoelectric unit (bulk heterojunction layer),and an electron transport layer.

(Organic EL Device)

For example, the organic EL device may have the following layerconfiguration (i) or (ii):

(i) anode/hole injection layer/hole transport layer/luminouslayer/electron transport layer/electron injection layer/cathode; or

(ii) anode/hole injection layer/hole transport layer/luminous layer/holeblocking layer/electron transport layer/electron injectionlayer/cathode.

The organic EL device may further be provided with other layer(s)containing functional organic compounds, such as an electron blockinglayer. The organic EL device may have a tandem structure (multiphotonstructure) composed of repeating units of organic functional layersdeposited on an electron injection layer through charge generatinglayers.

Examples of the charge-transporting thin film include a hole injectionlayer, a hole transport layer, an electron blocking layer, a luminouslayer, a hole blocking layer, an electron transport layer, and anelectron injection layer.

(Organic Thin-Film Solar Cell)

(Structure of Organic Photoelectric Device and Solar Cell)

The organic photoelectric device includes both devices for convertingelectric energy into light and devices for converting light intoelectric energy. Typical examples of the former include light-emittingdiodes and semiconductor laser devices, and typical examples of thelatter include photodiodes and solar cells.

For example, a solar cell having a single structure including a bulkheterojunction organic photoelectric device (i.e. a structure composedof a single bulk heterojunction layer) may have the following layerconfiguration (i):

(i) substrate/transparent electrode (anode)/hole transportlayer/photoelectric unit (bulk heterojunction layer)/electron transportlayer/counter electrode (cathode).

The bulk heterojunction photoelectric device is formed by laminating atransparent electrode (anode), a hole transport layer, a bulkheterojunction layer as a photoelectric unit, an electron transportlayer, and a counter electrode (cathode) in sequence onto one side of asubstrate.

The substrate is an element to support the transparent electrode, thephotoelectric unit, and the counter electrode which are laminatedthereon in sequence. In the present embodiment, since the incident lightto be subjected to photoelectric conversion enters the substrate, thesubstrate is composed of a material which can transmit the light to besubjected to photoelectric conversion, that is, a material which istransparent to the wavelength of the light to be subjected tophotoelectric conversion. The substrate may be, for example, a glasssubstrate or a resin substrate. The substrate is not an essentialelement. For example, a bulk heterojunction organic photoelectric devicemay be produced by depositing a transparent electrode and a counterelectrode on both sides of the photoelectric unit.

The photoelectric unit is a layer which converts light energy intoelectric energy, and is composed of a bulk heterojunction layercontaining a homogeneous mixture of p-type and n-type semiconductormaterials. P-type semiconductor materials function relatively as anelectron donor (donor), and n-type semiconductor materials functionrelatively as an electron acceptor (acceptor). As used herein, the terms“electron donor” and “electron acceptor” refer to “an electron donor andan electron acceptor which form a hole-electron pair (charge separationstate) via electron transfer from the electron donor to the electronacceptor due to light absorption”. In other words, they donate or acceptelectrons via a photoreaction, unlike electrodes that simply donate oraccept electrons.

The light incident on the transparent electrode through the substrate isabsorbed by an electron acceptor or an electron donor in the bulkheterojunction layer as the photoelectric unit. An electron istransferred from the electron donor to the electron acceptor to form ahole-electron pair (charge separation state). The generated charge istransported by an internal electric field (for example, the electricpotential difference between the transparent electrode and the counterelectrode, if they have different work functions). An electron passesthrough electron acceptors, while a hole passes through electron donors,and they are respectively transported to different electrodes. Aphotocurrent is thus detected. For example, if the transparent electrodehas a work function higher than that of the counter electrode, electronsare transported to the transparent electrode, while holes aretransported to the counter electrode. If the transparent electrode andthe counter electrode have reverse levels of work function, electronsand holes are respectively transported to reverse directions. Thedirections of transportation of electrons and holes can be controlled byapplying a potential across the transparent electrode and the counterelectrode.

(Dye-Sensitized Solar Cell)

For example, the dye-sensitized solar cell may have the following layerconfiguration (i):

(i) electrically conductive support/photosensitive layer/charge transferlayer/counter electrode.

When the solar cell of the invention is irradiated with sunlight orelectromagnetic waves equivalent to sunlight, the sensitizing dyeadsorbed on a semiconductor photoelectric material absorbs the incidentlight or electromagnetic waves and is excited. Electrons generated bythe excitation of the dye transfer to the semiconductor, pass throughthe electrically conductive support to the counter electrode, and thenreduce the redox electrolyte in the charge transfer layer. Meanwhile,materials (functional organic compounds) of the organic solar cell ofthe present invention are oxidized by transfer of electrons to thesemiconductor, and are then reduced to the original state by electronssupplied from the counter electrode through the charge transfer layer.As a result, the redox electrolyte in the charge transfer layer alsoreturns to the oxidized state that can be reduced again by electronssupplied from the counter electrode. Electrons flow in this way. A solarcell including a photoelectric device of the present invention may havesuch a structure.

(Organic Thin-Film Transistor)

FIG. 8A to FIG. 8F each show a structure of an organic thin-filmtransistor. FIG. 8A shows a structure of a field effect transistormanufactured by depositing a material, such as a metal foil onto asupport 6 to form a source electrode 2 and a drain electrode 3; forminga charge-transporting thin film (organic semiconductor layer 1) composedof organic thin-film transistor materials, i.e. functional organiccompounds of the present invention, between the two electrodes;depositing an insulation layer 5 on the organic semiconductor layer 1;and then depositing a gate electrode 4 on the insulating layer 5. FIG.8B shows a structure of the organic semiconductor layer 1 formed by aprocess such as coating so as to entirely cover the electrodes and thesurface of the support, unlike the organic semiconductor layer 1provided between the electrodes in the structure shown in FIG. 8A. FIG.8C shows a structure in which an organic semiconductor layer 1 is firstformed on a support 6 by a process such as coating, and a sourceelectrode 2, a drain electrode 3, an insulation layer 5, and a gateelectrode 4 are then formed thereon.

FIG. 8D shows a structure in which a material such as metal foil isdeposited onto a support 6 to form a gate electrode 4; an insulationlayer 5 is then formed thereon; a material such as metal foil isdeposited thereon to form a source electrode 2 and a drain electrode 3;and then an organic semiconductor layer 1 is formed between theelectrodes with an organic thin-film transistor material according tothe present invention. FIG. 8E and FIG. 8F show other exemplarystructures of the organic thin-film transistor of the present invention.

FIG. 9 shows an example schematic equivalent circuit diagram of organicTFT sheet.

An organic TFT sheet 10 includes a matrix of many organic TFTs 11. EachTFT 11 has a gate bus line 7 and a source bus line 8. Each TFT 11 has asource electrode connected to an output device 12 that is a liquidcrystal or electrophoretic device, for example, and constitutes pixelsof the display device. Pixel electrodes may be used as input electrodesof photosensors. In the example shown in FIG. 9, a liquid crystal deviceas an output device is represented by an equivalent circuit including aresistor and a capacitor. FIG. 9 shows a storage capacitor 13, avertical drive circuit 14, and a horizontal drive circuit 15.

(Electrically Conductive Sheet)

Examples of the electrically conductive sheet include sheet organic ELdevices, organic thin-film solar cells, dye-sensitized solar cells, andorganic thin-film transistors.

<<Functional Organic Compounds>>

The functional organic compound of the present invention is contained inthe thin charge transport film layer described above. Specific examplesof the functional organic compound include luminescent dopants, hostcompounds, hole transport materials, electron transport materials,organic solar cell materials, organic thin-film transistor materials,and solvents. The functional organic compound of the present inventionis preferably a material that can transport charge carriers (generalterm including electrons and holes), among these examples.

The one or more types of functional organic compounds having chiralelements of the present invention are contained in thecharge-transporting thin film, and the total of the number of chiralelements per molecule in each type of the functional organic compounds,when summed over all types of the functional organic compounds, is fouror more.

If any two molecules in the functional organic compounds of the presentinvention have identical two-dimensional representation of molecularstructure, these molecules are regarded as the same type. For example,enantiomers are counted as the same type.

The total of the number of chiral elements per molecule summed over alltypes of the functional organic compounds is preferably within a rangeof five to fifteen, in view of increase in entropy.

From the viewpoints of types of compounds, the electronic device of thepresent invention preferably contains at least two types of thefunctional organic compounds having chiral elements, and each of the atleast two types of the functional organic compounds includes at leastone isomer selected from the enantiomers and diastereomers. In anotherpreferred embodiment, the electronic device contains at least two typesof the functional organic compounds having chiral elements, and at leastone of the functional organic compounds has two or more chiral elementsper molecule, and thereby includes both enantiomers and diastereomers.

In another preferred embodiment, the electronic device contains at leasttwo types of the functional organic compounds having chiral elements, atleast one of the functional organic compounds is a metal complex; andthe metal complex has two or more chiral elements per molecule, andthereby includes both enantiomers and diastereomers. In a furtherpreferred embodiment, the electronic device contains at least two typesof the functional organic compounds having chiral elements, and all ofthe at least two types of the functional organic compounds include twoor more chiral elements per molecule, and thereby include bothenantiomers and diastereomers.

The one or more types of functional organic compounds preferably have abiaryl structure which has chiral elements due to hindered rotationbetween two aryl moieties, such that the functional organic compoundsinclude an atropisomer. Such an embodiment is preferred because thefunctional organic compound includes isomers with identical energylevels.

The term “chiral element due to hindered rotation” refers to a site ofbond forming a rotational axis in which free rotation of over 180° ishindered at a normal temperature and under normal pressure. If amolecule has a structure in which a bond forming a rotational axis ishindered in free rotation of over 180° according to its molecular model,the molecule is defined as a molecule having a chiral element due tohindered rotation. A usable molecule model is a Chem-Tutor studentmodelling system (available from SIGMA-ALDRICH Co.).

The functional organic compound having chiral elements of the presentinvention is preferably an aromatic hydrocarbon derivative or aheteroaromatic hydrocarbon derivative. The functional organic compoundsof the present invention are preferably aromatic hydrocarbon derivativesor heteroaromatic hydrocarbon derivatives, each of which preferably havethree or more aromatic rings and/or heteroaromatic rings in total.Examples of the aromatic hydrocarbon derivative include benzene,naphthalene, anthracene, tetracene, pentacene, chrycene, and helicene.Examples of the heteroaromatic hydrocarbon derivative include furan,thiophene, pyrrole, oxazole, thiazole, imidazole, benzofuran,benzothiophene, indole, dibenzofuran, dibenzothiophene, carbazole,pyridine, pyrazine, pyrimidine, and carboline.

The functional organic compounds having chiral elements are preferablycontained in a layer within the charge-transporting thin film at a totalcontent of 10% by mass or more, more preferably 20% by mass or more, themost preferably 50% by mass or more.

Specific examples of the functional organic compound will now bedescribed.

(Luminescent Dopant)

The at least one of the functional organic compounds having chiralelements is preferably a compound which emits light by excitation underan electric field. The compound which emits light by excitation under anelectric field is preferably a metal complex.

Examples of such a functional organic compound include luminescentdopants.

The luminescent dopant may be a fluorescent dopant or a phosphorescentdopant, and is preferably a phosphorescent dopant.

(Phosphorescent Dopant)

The luminescent dopant is preferably a phosphorescent dopant, from theviewpoint of higher luminous efficiency. The phosphorescent dopant is acompound which can emit light from the excited triplet state and whichhas a phosphorescence quantum yield of 0.01 or more at 25° C. Thephosphorescence quantum yield is preferably 0.1 or more.

A phosphorescent dopant can emit light on the basis of one of thefollowing two mechanisms. One emission mechanism is based on energytransfer, which involves: the recombination of carriers on a hostcompound onto which the carriers are transferred to produce an excitedstate of the host compound; and then light emission from aphosphorescent dopant due to transfer of this energy to thephosphorescent dopant. The other emission mechanism is based on acarrier trap, in which a phosphorescent dopant serves as a carrier trapto cause recombination of carriers on the phosphorescent dopant, andthereby light emission from the phosphorescent dopant occurs. In eachcase, it is essential that the energy in the excited state of thephosphorescent dopant be lower than that in the excited state of thehost compound.

The phosphorescent dopant is preferably a metal complex. Examples of themetal complex include those which contain a transition metal as centralmetal. Specifically, the metal complex preferably contains Cu, Ag, Pd,Rh, Ru, Au, Pt, Ir, or Os, more preferably Cu, Au, Pt, or Ir, as centralmetal. The metal complex preferably has two or more chiral elements permolecule, and thereby includes both enantiomers and diastereomers.

Preferred examples of the functional organic compound having chiralelements applicable to the present invention as luminescent dopant areas follows.

In the following structural formulae, the symbol “*” represents anasymmetric carbon atom as a chiral element, and the bold line representsa bond axis which is rotationally hindered to be a chiral element.

(2) Host Compound

“Host compound” refers to a compound which causes a luminescent dopantto emit light by energy transfer and electron transfer from its excitedstate to the luminescent dopant. A host compound also has a function tohelp stable dispersion of a luminescent dopant in a luminous layer.

The luminous efficiency can be increased by a traditional techniqueusing a host compound having a polycyclic aromatic fused ring.Unfortunately, if many host compounds having polycyclic aromatic fusedrings are used to increase the luminous efficiency, the host compoundsaggregate to cause uneven dispersion of a luminous dopant, resulting infailure to an increase in luminous efficiency and lifetime.

Specifically, conventional film formation of a luminous layer involves atradeoff between densification of the film with a host compound for anincreased lifetime and stable dispersion of luminescent molecules forincreased luminous efficiency. Even if intermediate compounds whichsolve the tradeoff are simply used, there have been limitations indesired improvements in characteristics. Use of a host compound of thepresent invention can maintain the stability of the luminous layer evenif the host compound is contained at high packing density, whichachieves both increased luminous efficiency and a prolonged lifetime.

Preferred examples of the functional organic compound having chiralelements applicable to the present invention as a host compound are asfollows.

(Electron Transport Material)

“Electron transport material” refers to materials having electrontransportability. A charge-transporting thin film containing such anelectron transport material includes an electron transport layer, anelectron injection layer, and a hole blocking layer in a broad sense.

Preferred examples of the functional organic compound having chiralelements applicable to the present invention as electron transportmaterial are as follows.

(Hole Transport Material)

“Hole transport material” refers to materials having holetransportability. A charge-transporting thin film containing such a holetransport material includes a hole transport layer, a hole injectionlayer, and an electron blocking layer in a broad sense.

Preferred examples of the functional organic compound having chiralelements applicable to the present invention as hole transport materialare as follows.

(Fluorescent Material)

Preferred examples of the functional organic compound having chiralelements applicable to the present invention as fluorescent material areas follows.

(Organic Solar Cell Material)

Preferred examples of the functional organic compound having chiralelements applicable to the present invention as organic solar cellmaterial are as follows.

(Solvent)

In a preferred embodiment, the charge-transporting thin film containsthe one or more types of functional organic compounds having chiralelements; and a volatile organic material having a boiling point lowerthan 300° C. under normal pressure, wherein the volatile organicmaterial has an asymmetric carbon atom.

Each of the functional organic compounds contained in thecharge-transporting thin film preferably includes a mixture of theenantiomers and diastereomers; the charge-transporting thin film furtherpreferably contains a volatile organic material having a boiling pointlower than 300° C. under normal pressure; and the volatile organicmaterial preferably has an asymmetric carbon atom.

Examples of applicable volatile organic material having a boiling pointlower than 300° C. under normal pressure and having an asymmetric carbonatom include hydrocarbon solvents having an asymmetric carbon atom. Morepreferable examples are aliphatic hydrocarbon solvents, aromatichydrocarbon solvents, and halogen solvents.

Specific examples of the volatile organic material of the presentinvention include substituted aliphatic hydrocarbon solvents havingasymmetric carbon atoms (e.g. acyclic aliphatic hydrocarbon solvent,such as hexane and heptane; cyclic aliphatic hydrocarbon solvent, suchas cyclohexane; alcohol solvents, such as methanol, ethanol, n-propanol,and ethylene glycol; ketone solvents, such as acetone and methyl ethylketone; and ether solvents, such as diethyl ether, diisopropyl ether,tetrahydrofuran, 1,4-dioxane, and ethylene glycol monomethyl ether);substituted aromatic hydrocarbon solvents having asymmetric carbon atoms(e.g. toluene, xylene, mesitylene, cyclohexylbenzene, andisopropylbiphenyl); and substituted halogen solvents having asymmetriccarbon atoms (e.g. methylene chloride, 1,1,2-trichloroethane, andchloroform). More specific examples include 2-ethylhexane, sec-butylether, 2-pentanol, 2-methyltetrahydrofuran, 2-propylene glycolmonomethyl ether, 2,3-dimethyl-1,4-dioxane, sec-butylbenzene,4-(sec-butyl)biphenyl, and 2-methylcyclohexylbenzene.

The functional organic compounds of the present invention as describedabove may be used to form a charge-transporting thin film of the presentinvention, in combination with any known functional compoundcorresponding to each function of the layer, provided that theadvantageous effect of the present invention is not impaired.

<<Process for Forming Charge-Transporting Thin Film>>

A process for forming the charge-transporting thin film (such as holeinjection layer, hole transport layer, electron blocking layer, luminouslayer, hole blocking layer, electron transport layer, and electroninjection layer) of the present invention will now be described.

The charge-transporting thin film of the present invention may be formedby any conventional method, including vacuum vapor deposition and wetprocesses.

Examples of the wet process include spin coating, casting, ink jetting,printing, die coating, blade coating, roller coating, spray coating,curtain coating, and Langmuir Blodgett (LB) coating. Thecharge-transporting thin film of the present invention is preferablyformed by a process suitable for a roll-to-roll process, such as diecoating, roller coating, ink jetting, or spray coating, from theviewpoints of uniformity and productivity of the layer.

Examples of solvent used to dissolve or disperse the functional organiccompounds according to the present invention include ketones, such asmethyl ethyl ketone and cyclohexanone; fatty acid esters, such as ethylacetate; halogenated hydrocarbons, such as dichlorobenzene; aromatichydrocarbons, such as toluene, xylene, mesitylene, andcyclohexylbenzene; aliphatic hydrocarbons, such as cyclohexane,decaline, and dodecane; and organic solvents, such as DMF and DMSO.

The functional organic compounds can be dispersed by any method, such asultrasonic wave dispersion, high-shearing force dispersion, or mediadispersion.

The individual layers may be deposited by different processes. If avapor deposition process is employed for film formation, the depositionconditions vary depending on compounds to be used, and are preferablyselected appropriately from the following general ranges: a boat heatingtemperature of 50 to 450° C., a degree of vacuum of 10⁻⁶ to 10⁻² Pa, adeposition rate of 0.01 to 50 nm per second, a substrate temperature of−50 to 300° C., and a layer thickness of 0.1 nm to 5 μm, preferablywithin the range of 5 to 200 nm.

In production of such a charge-transporting thin film of the presentinvention, all layers from the hole injection layer to the cathodeshould preferably be formed in a single vacuuming operation; however, asemi-finished film may be taken out for a different deposition process.In such a case, the process should be performed under a dry inactive gasatmosphere.

The charge-transporting thin film of the present invention containingfunctional organic compounds may have any appropriate thickness whichvaries among layers and is preferably within a range of 0.1 nm to 5 μm,preferably within a range of 5 to 200 nm.

<<Anode>>

The anode to apply electric fields to the charge-transporting thin filmis preferably composed of an electrode material having a high workfunction (4 eV or higher, preferably 4.5 V or higher) such as a metal,an alloy, an electrically conductive compound, or a mixture thereof.Specific examples of such an electrode material include metals such asAu; and electrically conductive transparent materials such as CuI,indium-tin oxide (hereinafter, abbreviated as “ITO”), SnO₂, and ZnO.Amorphous materials applicable to production of a transparentelectrically conductive film, such as IDIXO (In₂O₃—ZnO), may also beused.

The anode may also be produced by depositing the electrode material intoa thin film by any process such as vapor deposition or sputtering, andthen producing a desired pattern by any process such asphotolithography. If high patterning accuracy (approximately 100 μm orhigher) is not required, the pattern may be formed through a mask havinga desired shape by vapor deposition or sputtering of the electrodematerial.

Alternatively, the film may be formed with a coating material, such asan organic conductive compound, through a wet process, for example,printing or coating. If luminescent light is extracted from the anode,the anode preferably has a transmittance of above 10%. The sheetresistance of the anode is preferably several hundred ohms or lower persheet.

The thickness of the anode is normally within the range of 10 nm to 1μm, preferably within the range of 10 to 200 nm, although it depends onthe electrode material.

<<Cathode>>

The cathode of the present invention is preferably composed of anelectrode material having a low work function (4 eV or lower), such as ametal (referred to as “electron-injecting metal”), an alloy, anelectrically conductive compound, or a mixture thereof. Specificexamples of such an electrode material include sodium, sodium-potassiumalloys, magnesium, lithium, magnesium/copper mixtures, magnesium/silvermixtures, magnesium/aluminum mixtures, magnesium/indium mixtures,aluminum/aluminum oxide (Al₂O₃) mixtures, indium, lithium/aluminummixtures, aluminum, and rare earth metals. From the perspective ofelectron injection and resistance to oxidation, it is preferable to usea mixture of a metal as an electron-injecting metal and a second metalwhich is a stable metal with a higher work function than theelectron-injecting metal, among these materials. Preferred examples ofsuch a mixture include magnesium/silver mixtures, magnesium/aluminummixtures, magnesium/indium mixtures, aluminum/aluminum oxide (Al₂O₃)mixtures, lithium/aluminum mixtures, and aluminum.

The cathode can be produced by depositing such an electrode materialinto a thin film using any process, for example, vapor deposition orsputtering. The sheet resistance of the cathode is preferably severalhundred ohms or lower per sheet. The thickness of the cathode isnormally within the range of 10 nm to 5 μm, preferably within the rangeof 50 to 200 nm.

After any of the metals exemplified above is deposited into a thin filmwith a thickness of 1 to 20 nm on a cathode, any of the transparentconductive materials exemplified in the description of the anode isdeposited thereon to produce a transparent or translucent cathode. Thisprocess can be applied to production of a device having an anode and acathode that have transparency.

<<Support Substrate>>

The support substrate (hereinafter, also referred to as “substrate” or“support”) of the organic EL device, organic thin-film solar cell, anddye-sensitized solar cell including the charge-transporting thin film ofthe present invention may be any type of substrate, for example, glassor plastic substrate, and may be transparent or opaque. In the case ofan organic EL device, if light is extracted from the support substrate,the support substrate is preferably transparent. Examples of thepreferred transparent support substrate include glass, quartz, andtransparent resin films. In particular, the support substrate ispreferably a resin film which can provide a flexible organic EL device.

Examples of the resin film include polyesters, such as poly(ethyleneterephthalate) (PET) and poly(ethylene naphthalate) (PEN); polyethylene;polypropylene; cellophane; cellulose esters and derivatives thereof,such as cellulose diacetate, cellulose triacetate (TAC), celluloseacetate butyrate, cellulose acetate propionate (CAP), cellulose acetatephthalate, and cellulose nitrate; poly(vinylidene chloride); poly(vinylalcohol); poly(ethylene-vinyl alcohol); syndiotactic polystyrene;polycarbonates; norbornene resins; polymethylpentene; polyether ketone;polyimides; polyethersulfones (PESs); polyphenylene sulfide;polysulfones; polyether imides; polyether ketone imides; polyamides;fluororesins; nylons; poly(methyl methacrylate); acrylics orpolyarylates; and cycloolefin resins, such as ARTON (product name;manufactured by JSR) and APEL (product name; manufactured by MitsuiChemicals, Inc.).

The surface of the resin film may be covered with a coating layer of aninorganic or organic material or a hybrid film of inorganic and organicmaterials. The resin film is preferably a barrier film having watervapor permeability (measured in accordance with JIS K 7129-1992 (25±0.5°C.; relative humidity: (90±2)% RH)) of 1×10⁻² g/(m²·24 h) or lower, andis preferably a high barrier film having oxygen permeability (measuredin accordance with JIS K 7126-1987) of 1×10⁻³ cm³/(m²·24 h·atm) or lowerand water vapor permeability of 1×10⁻⁵ g/(m²·24 h) or lower.

The barrier film may be composed of any material that can blockinfiltration of substances, such as moisture and oxygen, which causedeterioration of the electronic device. For example, silicon oxide,silicon dioxide and silicon nitride can be used. In order to prevent thebrittleness of the film, the film preferably has a laminated structurecomposed of one or more inorganic layers and organic layers. Theinorganic layers and organic layers may be deposited in any order,preferably alternately.

The barrier film may be formed by any process, for example, vacuum vapordeposition, sputtering, reactive sputtering, molecular beam epitaxy,cluster ion beam deposition, ion plating, plasma polymerization,atmospheric pressure plasma polymerization, plasma chemical vapordeposition (CVD), laser CVD, thermal CVD, and coating. In particular,the gas barrier film is preferably produced by an atmospheric pressureplasma polymerization process as described in Japanese PatentApplication Laid-Open Publication No. 2004-68143.

Examples of an opaque support substrate include metal plates such asaluminum plate and stainless steel plate, films, opaque resinsubstrates, and ceramic substrates.

<<Sealing>>

Examples of a sealing means applicable to the organic EL device, organicthin-film solar cell and dye-sensitized solar cell including thecharge-transporting thin film of the present invention include adhesionof a sealing material, electrodes, and a support substrate with anadhesive. The sealing material may have a concave or flat shape, andtransparency and electric insulation are no object.

Specific examples of the sealing material include glass plates, apolymer plate or film, and a metal plate or film. Specific examples ofmaterials for the glass plate include soda-lime glass,barium-strontium-containing glass, lead glass, aluminosilicate glass,borosilicate glass, barium borosilicate glass, and quartz. Examples ofmaterials for the polymer plate include polycarbonates, acrylics,poly(ethylene terephthalate), polyether sulfides, and polyethersulfones. Examples of materials for the metal plate include one or moretypes of metals or alloys selected from the group consisting ofstainless steel, iron, copper, aluminum, magnesium, nickel, zinc,chromium, titanium, molybdenum, silicone, germanium and tantalum.

In the present invention, a polymer film and a metal film may bepreferably used as a sealing material. The polymer film preferably hasan oxygen permeability (measured in accordance with JIS K 7126-1987) of1×10⁻³ cm³/(m²·24 h·atm) or lower and a water vapor permeability(measured in accordance with JIS K 7129-1992; 25±0.5° C., relativehumidity: (90±2) %) of 1×10⁻³ g/(m²/24 h) or lower.

The sealing material may be processed into a concave shape through anyprocess, for example, sandblasting or chemical etching.

Specific examples of the adhesive for sealing include light-curable orthermosetting adhesives having reactive vinyl groups, such as acrylicacid oligomers and methacrylic acid oligomers; moisture-curable resins,such as 2-cyanoacrylic acid esters; thermosetting and chemically curableadhesives (two-component adhesives), such as epoxy adhesives; hot-meltadhesives, such as polyamide adhesives, polyester adhesives, andpolyolefin adhesives; and cation-curable and ultraviolet-curable epoxyresin adhesives.

<<Protective Film and Protective Plate>>

In order to enhance the mechanical strength of the electronic device, aprotective film or plate may be provided on the outer face of thesealing film, the outer face being remote from the support substrateacross the organic layer. In particular, since sealing with a sealingfilm does not always ensure high mechanical strength of the electronicdevice, such a protective film or plate is preferably provided whensealing is processed with the sealing film. Examples of a materialusable for such a protective film or plate include the same glassplates, a polymer plate or film, and a metal plate or film as thosewhich can be used for the sealing. A polymer film is preferably used,from the perspective of weight reduction and thinning of the electronicdevice.

<Example of Impedance Spectroscopic Measurement for Resistance of ThinFilm>

In impedance spectroscopy (hereinafter, also referred to as IS), asmall-amplitude sinusoidal voltage signal is applied to an organicelectroluminescent element, impedance is calculated based on theamplitude and the phase of the current response signal to determineimpedance spectrum as a function of frequency of the applied voltagesignal.

The impedance thus determined is plotted versus frequency of the appliedvoltage signal as parameter in a complex plane. Such a plot is referredto as Cole-Cole plot. Basic transfer functions, i.e. modulus,admittance, and permittivity functions, can be determined based on theimpedance. A transfer function suitable for the purpose of analysis canbe selected from these four transfer functions (see “ImpedanceSpectroscopy of Organic Electronic Devices”, OYO BUTURI, Vol. 76, No. 11(2007), pp. 1252-1258).

In the present invention, the modulus plot (hereinafter, referred to as“M-plot”) was employed. Reciprocals of capacitance components aredetermined based on the M-plot. In the M-plot, a diameter of an arc-likepart of the plot corresponds to a reciprocal of capacitance of a layer,and is proportional to a film thickness. Thus, variations in filmthickness can also be detected.

In the IS analysis, in general, an equivalent circuit of an organicelectroluminescent element is deduced from the trajectory of theCole-Cole plot, and a trajectory of the Cole-Cole plot calculated basedon the deduced equivalent circuit corresponding to the observed data isretrieved to determine the equivalent circuit.

The IS measurement can be performed with Solartron Impedance Analyzer1260 and Solartron 1296 dielectric interface (manufactured bySolartron), for example, superimposing an AC voltage of 30 to 100 mVrms(frequency range: 0.1 mHz to 10 MHz) onto a DC voltage.

The equivalent circuit analysis can be performed with ZView softwaremanufactured by Scribner Associates, Inc.

The impedance spectroscopy is applied to determine a resistance of aspecific layer in an organic EL device (having the following layerconfiguration: ITO/HIL (hole injection layer)/HTL (hole transportlayer)/EML (luminous layer)/ETL (electron transport layer)/EIL (electroninjection layer)/AI). The method of determination is now described. Forexample, in calculation of the resistance of the electron transportlayer (ETL), devices which differ only in the thickness of ETL areproduced and compared for M-plot to determine which portion of the curvein the plot corresponds to ETL.

FIG. 10 shows an example of an M-plot of organic EL devices withdifferent thicknesses of the electron transport layer, that is, of 30nm, 45 nm, and 60 nm, respectively. The vertical axis represents theimaginary part M″ (1/nF), and the horizontal axis represents the realpart M′ (1/nF).

The resistance (R) determined from this plots are then plotted versusthe thickness of ETL as shown in FIG. 11. Since the plot is almostlinear, the resistance value at each layer thicknesses can be determinedfrom the plot.

FIG. 11 shows an example relation between the thickness and theresistance of the ETL. Since the plot is almost linear, the resistancevalue at each layer thicknesses can be determined based on the relationbetween the thickness and the resistance of the ETL shown in FIG. 11.

FIG. 12 shows an equivalent circuit model of an organic EL device havingthe following layer configuration: ITO/HIL/HTL/EML/ETL/AI, and FIG. 13shows example analytical results for each layer, indicating the relationbetween the resistance and the voltage for each layer.

Meanwhile, the same organic EL device was deteriorated by emitting lightfor a long time, and was then measured under the same conditions. Theresults are overlaid with each other, as shown in FIG. 14. Themeasurement values for each layer at a voltage of 1 V are shown in Table2. FIG. 14 shows example analytical results of an organic EL deviceafter deterioration.

TABLE 2 HIL(Ω) ETL(Ω) HTL(Ω) EML(Ω) Before driving 1.1k 0.2M 0.2 G 1.9 GAfter deterioration 1.2k 5.7M 0.3 G 2.9 G

The results indicate that only the ETL in the organic EL device afterdeterioration has a significantly increased resistance. Specifically,the resistance of the ETL increased to approximately 30 times at a DCvoltage of 1 V.

The method described above can be employed to calculate variations inresistance after application of current as described in the Examples ofthe present invention.

EXAMPLES

The present invention will now be described in more detail by way ofExamples. The present invention however should not be limited to theseExamples. Throughout the Examples, “part(s)” and the symbol “%” indicate“part (s) by mass” and “% by mass” unless otherwise stated.

The compounds used in the Examples are as follows:

Example 1

In the Example below, the charge-transporting thin film is a luminouslayer, and the functional organic compounds are a luminescent dopant anda host compound.

<<Preparation of Organic EL Device 1-1>>

Indium tin oxide (ITO) with a thickness of 100 nm was deposited on aglass substrate with dimensions of 100 mm by 100 mm by 1.1 mm (NA 45manufactured by NH Technoglass Corporation) and was patterned into ananode. A transparent support substrate provided with the transparent ITOelectrode was ultrasonically cleaned in isopropyl alcohol, was dried ina dry nitrogen stream, and then was cleaned in a UV ozone environmentfor five minutes.

A solution of 70% poly(3,4-ethylenedioxythiophene)-polyethylenesulfonate (hereinafter, referred to asPEDOT/PSS; Baytron P Al 4083 available from Bayer) in pure water wasapplied by spin coating on the transparent support substrate at 3000 rpmfor 30 seconds. The coating film was dried at 200° C. for one hour. Ahole injection layer with a thickness of 20 nm was thereby formed.

The transparent support substrate was fixed to a substrate holder in acommercially available vacuum vapor deposition system, and 200 mg ofα-NPD (4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl) was placed onto amolybdenum resistive heating boat, 200 mg of CBP(4,4′-N,N′-dicarbazole-biphenyl) was placed onto another molybdenumresistive heating boat, 200 mg of compound D-9 was placed onto anothermolybdenum resistive heating boat, and 200 mg of BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) was placed onto anothermolybdenum resistive heating boat. The molybdenum resistive heatingboats were then placed in the vacuum vapor deposition system.

After evacuation of the vacuum vessel to 4×10⁻⁴ Pa, the heating boatcontaining α-NPD was electrically heated to deposit α-NPD onto the holeinjection layer at a deposition rate of 0.1 nm/sec. A hole transportlayer with a thickness of 30 nm was thereby formed.

The heating boats respectively containing CBP and D-9 were electricallyheated to codeposit CBP and D-9 onto the hole transport layer atdeposition rates of 0.1 nm/sec and 0.010 nm/sec, respectively. Aluminous layer with a thickness of 40 nm was thereby formed.

The heating boat containing BCP was then electrically heated to depositBCP onto the hole blocking layer at a deposition rate of 0.1 nm/sec. Anelectron transport layer with a thickness of 30 nm was thereby formed.

Subsequently, lithium fluoride was deposited into a thickness of 0.5 nmto form a cathode buffer layer, and then aluminum was deposited into athickness of 110 nm to form a cathode. The organic EL device 1-1 wasthereby prepared.

<<Preparation of Organic EL Devices 1-2 to 1-52>>

The organic EL devices 1-2 to 1-52 were prepared as in the organic ELdevice 1-1, except that CBP and D-9 were replaced with the individualcompounds described in Table 1.

<<Evaluation of Organic EL Devices 1-1 to 1-52>>

For evaluation of the resulting organic EL devices, lighting devicesshown in FIG. 15 and FIG. 16 were produced with the organic EL devices,and were analyzed for variations in resistance of the luminous layer asmeasured with an impedance spectrometry system and in half-width of theemission spectrum of the organic EL device.

FIG. 15 is a diagrammatic view of a lighting device. The organic ELdevice 101 including the charge-transporting thin film of the presentinvention is covered with a glass case 102 (sealing with the glass case102 is performed under a high-purity (99.999% or higher) nitrogen gasatmosphere in a glovebox to avoid exposure of the organic EL device 101to the air). Specifically, an epoxy photo-curable adhesive (LUXTRACKLC0629B, manufactured by TOAGOSEI CO., LTD.) as a sealant was appliedonto the periphery of the glass case, where the glass case is in touchwith the glass substrate provided with the organic EL device. The glasscase was attached on the transparent support substrate to cover thecathode. The adhesive was then cured by irradiation with UV lightincident on the side of the glass substrate, except the organic ELdevice.

FIG. 16 is a cross-sectional view of the lighting device that includes acathode 105, an organic EL layer 106, and a glass substrate 107 providedwith a transparent electrode. The interior of the glass cover 102 isfilled with nitrogen gas 108 and is provided with a water-trapping agent109.

(1) Variation in Resistance after Driving the Organic EL Device

The individual organic EL devices prepared as described above weresubjected to measurement of resistance of the luminous layer at a biasvoltage of 1 V with Solartron Impedance Analyzer 1260 and Solartron 1296dielectric interface (manufactured by Solartron), based on the methoddescribed in “Hakumaku no Hyoka Handbook (Handbook of Thin FilmCharacterization Technology)” (published by Technosystem Co., Ltd.) onpages 423 to 425.

The individual organic EL devices were driven for 1000 hours under aconstant current density of 2.5 mA/cm² at room temperature (25° C.), andwere subjected to measurement of the resistance of the luminous layerbefore and after the driving of the device. Based on the observedresults, a variation in resistance was calculated for each organic ELdevice by the expression below. Table 3 shows the variation inresistance of the individual organic EL devices as a relative value tothat (set as 100) of the organic EL device 1-1.Variation in resistance between before and after thedriving=Abs[{(resistance after the driving)/(resistance before thedriving)}−1]×100

The expression indicates that the variation in resistance between beforeand after the driving decreases as the value approaches 0.

(2) Variation in Half-Width of the Emission Spectrum of the Organic ELDevice Between Before and after the Driving

The individual organic EL devices were driven for 1000 hours under aconstant current density of 2.5 mA/cm² at room temperature (25° C.), andwere subjected to measurement of the emission spectrum before and afterthe driving of the device with a spectroradiometer CS-1000 (availablefrom Konica Minolta, Inc.). A variation in half-width to the peakwavelength was calculated for each organic EL device by the expressionbelow. Table 3 shows the variation in half-width of the individualorganic EL devices as a relative value to that (set as 100) of theorganic EL device 1-1.Variation in half-width between before and after thedriving=Abs[{(half-width after the driving)/(half-width before thedriving)}−1]×100

The expression indicates that the variation in half-width between beforeand after the driving decreases as the value approaches 0.

TABLE 3 Variation in resistance Variation in Total number DeviceLuminescent of luminous layer half-width of chiral No. Host dopant(relative value) (relative value) elements Remarks 1-1 CBP D-9 100 100 1*1 1-2 CBP D-111 92 80 3 *1 1-3 H-104 D-9 88 102 3 *1 1-4 H-104 D-101 1141 6 *2 1-5 H-104 D-102 12 32 9 *2 1-6 H-104 D-103 11 30 9 *2 1-7 H-104D-104 6 42 6 *2 1-8 H-104 D-105 5 48 9 *2 1-9 H-104 D-106 9 38 6 *2 1-10H-104 D-107 9 42 9 *2 1-11 H-104 D-108 13 48 6 *2 1-12 H-104 D-109 14 385 *2 1-13 H-104 D-110 13 35 6 *2 1-14 H-104 D-111 10 33 5 *2 1-15 H-104D-112 6 47 4 *2 1-16 H-104 D-113 13 36 4 *2 1-17 H-104 D-114 7 38 4 *21-18 H-104 D-115 8 46 4 *2 1-19 H-104 D-116 11 45 6 *2 1-20 H-104 D-11710 44 6 *2 1-21 H-104 D-118 8 40 4 *2 1-22 H-104 D-119 13 31 7 *2 1-23H-104 D-120 14 34 6 *2 1-24 H-104 D-121 13 44 4 *2 1-25 H-104 D-122 1134 4 *2 1-26 H-104 D-123 8 36 5 *2 1-27 H-104 D-124 7 41 4 *2 1-28 H-104D-125 7 40 6 *2 1-29 H-104 D-126 10 30 6 *2 1-30 H-104 D-127 11 38 6 *21-31 H-104 D-128 9 44 9 *2 1-32 H-104 D-129 10 42 6 *2 1-33 H-104 D-13014 39 6 *2 1-34 H-101 D-101 13 39 5 *2 1-35 H-102 D-101 7 45 6 *2 1-36H-103 D-101 14 42 5 *2 1-37 H-105 D-101 10 36 5 *2 1-38 H-106 D-101 7 366 *2 1-39 H-107 D-101 6 44 5 *2 1-40 H-108 D-101 6 35 5 *2 1-41 H-109D-101 7 36 5 *2 1-42 H-110 D-101 11 29 6 *2 1-43 H-111 D-101 8 36 6 *21-44 H-112 D-101 8 34 5 *2 1-45 H-113 D-101 6 43 5 *2 1-46 H-114 D-10111 33 5 *2 1-47 H-115 D-101 12 49 5 *2 1-48 H-116 D-101 14 35 5 *2 1-49H-117 D-101 14 32 5 *2 1-50 H-118 D-101 14 40 8 *2 1-51 H-119 D-101 1140 6 *2 1-52 H-120 D-101 6 46 5 *2 *1: Comparative example *2: Presentinvention

The results shown in Table 3 indicate that the organic EL devices 1-4 to1-52 of the present invention undergo a smaller variation in resistanceof the luminous layer and half-width of the emission spectrum, ascompared to those of the organic EL devices 1-1 to 1-3 of thecomparative examples. Accordingly, the present invention provides anorganic EL device which barely undergoes variations in physicalproperties of the thin film, i.e. luminous layer.

Example 2

Another Example will now be described. In this example, thecharge-transporting thin film is a luminous layer, and the functionalorganic compounds are a luminescent dopant and a host compound, as inExample 1.

<<Preparation of Organic EL Device 2-1>>

Indium tin oxide (ITO) with a thickness of 100 nm was deposited on aglass substrate with dimensions of 100 mm by 100 mm by 1.1 mm (NA 45manufactured by NH Technoglass Corporation) and was patterned into ananode. A transparent support substrate provided with the transparent ITOelectrode was ultrasonically cleaned in isopropyl alcohol, was dried ina dry nitrogen stream, and then was cleaned in a UV ozone environmentfor five minutes.

A solution of 70% poly(3,4-ethylenedioxythiophene)-polyethylenesulfonate (PEDOT/PSS; Baytron P Al 4083available from Bayer) in pure water was applied by spin coating on thetransparent support substrate at 3000 rpm for 30 seconds. The coatingfilm was dried at 200° C. for one hour. A first hole transport layerwith a thickness of 20 nm was thereby formed.

The substrate was transferred into a nitrogen atmosphere, and a solutionof ADS254BE (Poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine];manufactured by American Dye Source, Inc.) (50 mg) dissolved in 10 ml ofmonochlorobenzene was coated by spin coating onto the first holetransport layer at 2500 rpm for 30 seconds, and the substrate was driedat 130° C. for one hour in the vacuum. A second hole transport layer wasthereby formed.

A solution of CBP (100 mg) and D-9 (13 mg) dissolved in 10 ml of butylacetate was coated by spin coating onto the second hole transport layerat 1000 rpm for 30 seconds, and the substrate was dried at 60° C. forone hour in the vacuum. A luminous layer with a thickness ofapproximately 45 nm was thereby formed.

A solution of BCP (50 mg) dissolved in 10 ml of Hexafluoroisopropanol(HFIP) was coated by spin coating onto the luminous layer at 1000 rpmfor 30 seconds, and the substrate was dried at 60° C. for one hour inthe vacuum. An electron transport layer with a thickness ofapproximately 25 nm was thereby formed.

The substrate was then fixed to a substrate holder in a vacuum vapordeposition system. After evacuation of the vacuum vessel to 4×10⁻⁴ Pa,potassium fluoride was deposited into a thickness of 0.4 nm to form acathode buffer layer, and then aluminum was deposited into a thicknessof 110 nm to form a cathode. The organic EL device 2-1 was therebyprepared.

<<Preparation of Organic EL Devices 2-2 to 2-52>>

The organic EL devices 2-2 to 2-52 were prepared as in the organic ELdevice 2-1, except that CBP and D-9 were replaced with the individualcompounds described in Table 2.

<<Evaluation of Organic EL Devices 2-1 to 2-52>>

The resulting organic EL devices were each sealed as in the sealing ofthe organic EL device 1-1 in Example 1 to produce a lighting deviceshown in FIG. 15 or FIG. 16, and the lighting device was analyzed.

The resulting samples were subjected to evaluation of variations inresistance of the luminous layer and in half-width of the emissionspectrum, as in the Example 1. Table 4 shows the variations inresistance of the luminous layer and in half-width of the emissionspectrum of the organic EL devices as relative values to those (set as100) of the organic EL device 2-1. The results are shown in Table 4.

TABLE 4 Variation in resistance of Variation in Total number DeviceLuminescent luminous layer half-width of chiral No. Host dopant(relative value) (relative value) elements Remarks 2-1 CBP D-9 100 100 1*1 2-2 CBP D-113 102 88 2 *1 2-3 H-102 D-9 81 90 3 *1 2-4 H-102 D-101 645 6 *2 2-5 H-102 D-102 4 57 9 *2 2-6 H-102 D-103 5 47 9 *2 2-7 H-102D-104 5 54 6 *2 2-8 H-102 D-105 8 47 9 *2 2-9 H-102 D-106 6 52 6 *2 2-10H-102 D-107 10 45 9 *2 2-11 H-102 D-108 15 57 6 *2 2-12 H-102 D-109 8 576 *2 2-13 H-102 D-110 18 48 6 *2 2-14 H-102 D-111 6 53 5 *2 2-15 H-102D-112 8 54 4 *2 2-16 H-102 D-113 5 46 4 *2 2-17 H-102 D-114 5 50 4 *22-18 H-102 D-115 11 56 4 *2 2-19 H-102 D-116 5 52 6 *2 2-20 H-102 D-11714 57 6 *2 2-21 H-102 D-118 16 53 4 *2 2-22 H-102 D-119 12 46 7 *2 2-23H-102 D-120 13 56 6 *2 2-24 H-102 D-121 8 50 4 *2 2-25 H-102 D-122 10 534 *2 2-26 H-102 D-123 12 46 5 *2 2-27 H-102 D-124 9 54 4 *2 2-28 H-102D-125 8 48 6 *2 2-29 H-102 D-126 10 45 6 *2 2-30 H-102 D-127 18 56 6 *22-31 H-102 D-128 16 52 9 *2 2-32 H-102 D-129 13 52 6 *2 2-33 H-102 D-13010 47 6 *2 *1: Comparative example *2: Present invention

The results shown in Table 4 indicate that the organic EL devices 2-4 to2-52 including the charge-transporting thin film of the presentinvention undergo a smaller variation in resistance of the luminouslayer and in half-width of the emission spectrum, as compared to thoseof the organic EL devices 2-1 to 2-3 of the comparative examples.Accordingly, the present invention provides an organic EL device whichbarely undergoes variations in physical properties of the thin film,i.e. luminous layer.

Example 3

Another Example will now be described. In this example, thecharge-transporting thin film is a luminous layer, and the functionalorganic compounds are a luminescent dopant and a host compound.

<<Preparation of Organic EL Device 3-1>>

Indium tin oxide (ITO) with a thickness of 100 nm was deposited on aglass substrate with dimensions of 100 mm by 100 mm by 1.1 mm (NA 45manufactured by NH Technoglass Corporation) and was patterned into ananode. A transparent support substrate provided with the transparent ITOelectrode was ultrasonically cleaned in isopropyl alcohol, was dried ina dry nitrogen stream, and then was cleaned in a UV ozone environmentfor five minutes.

The transparent support substrate was fixed to a substrate holder in acommercially available vacuum vapor deposition system, and 200 mg of TPD(N,N′-bis(3-methylphenyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine)was placed onto a molybdenum resistive heating boat, 200 mg of CBP wasplaced onto another molybdenum resistive heating boat, 200 mg ofcompound D-9 was placed onto another molybdenum resistive heating boat,and 200 mg of compound D-1 was placed onto another molybdenum resistiveheating boat, 200 mg of compound D-6 was placed onto another molybdenumresistive heating boat, and 200 mg of BCP was placed onto anothermolybdenum resistive heating boat. The molybdenum resistive heatingboats were then placed in the vacuum vapor deposition system.

After evacuation of the vacuum vessel to 4×10⁻⁴ Pa, the heating boatcontaining TPD was electrically heated to deposit TPD onto thetransparent support substrate at a deposition rate of 0.1 nm/sec. A holetransport layer with a thickness of 10 nm was thereby formed.

The heating boats respectively containing CBP, D-9, D-1, and D-6 wereelectrically heated to codeposit CBP, D-9, D-1, and D-6 onto the holetransport layer at deposition rates of 0.1 nm/sec, 0.025 nm/sec, 0.0007nm/sec, and 0.0002 nm/sec, respectively. A luminous layer with athickness of 60 nm was thereby formed.

The heating boat containing BCP was then electrically heated to depositBCP onto the luminous layer at a deposition rate of 0.1 nm/sec. Anelectron transport layer with a thickness of 20 nm was thereby formed.

Subsequently, potassium fluoride was deposited into a thickness of 0.5nm to form a cathode buffer layer, and aluminum was deposited into athickness of 110 nm to form a cathode. The organic EL device 3-1 wasthereby prepared.

The organic EL device 3-1 thus prepared was electrically driven, andemitted substantially white light, which indicates that the device canbe applied to a lighting device. An organic EL device containing othercompounds exemplified above also emitted white light.

<<Preparation of Organic EL Devices 3-2 to 3-52>>

The organic EL devices 3-2 to 3-52 were prepared as in the organic ELdevice 3-1, except that CBP and D-9 were replaced with the compoundsdescribed in Table 5.

<<Evaluation of Organic EL Devices 3-1 to 3-52>>

The individual organic EL devices were subjected to measurement ofvariations in resistance of the luminous layer, as in Example 1. Theresults demonstrate that the measured values for the organic EL devicesincluding the charge-transporting thin film of the present invention areless than half of those of the comparative examples. Table 5 shows thevariations in resistance of the luminous layer of the individual organicEL deices as relative values to that (set as 100) of the organic ELdevice 3-1.

TABLE 5 Variation in Total resistance of number of Device Luminescentluminous layer chiral No. Host dopant (relative value) elements Remarks3-1 CBP D-9 100 1 *1 3-2 CBP D-111 96 3 *1 3-3 H-104 D-9 92 3 *1 3-4H-104 D-101 15 6 *2 3-5 H-104 D-102 22 9 *2 3-6 H-104 D-103 17 9 *2 3-7H-104 D-104 33 6 *2 3-8 H-104 D-105 22 9 *2 3-9 H-104 D-106 29 6 *2 3-10H-104 D-107 26 9 *2 3-11 H-104 D-108 20 6 *2 3-12 H-104 D-109 31 6 *23-13 H-104 D-110 19 6 *2 3-14 H-104 D-111 26 5 *2 3-15 H-104 D-112 33 4*2 3-16 H-104 D-113 26 4 *2 3-17 H-104 D-114 19 4 *2 3-18 H-104 D-115 394 *2 3-19 H-104 D-116 31 6 *2 3-20 H-104 D-117 25 6 *2 3-21 H-104 D-11825 4 *2 3-22 H-104 D-119 22 7 *2 3-23 H-104 D-120 29 6 *2 3-24 H-104D-121 17 4 *2 3-25 H-104 D-122 22 4 *2 3-26 H-104 D-123 28 5 *2 3-27H-104 D-124 18 4 *2 3-28 H-104 D-125 30 6 *2 3-29 H-104 D-126 34 6 *23-30 H-104 D-127 22 6 *2 3-31 H-104 D-128 20 9 *2 3-32 H-104 D-129 19 6*2 3-33 H-104 D-130 31 6 *2 3-34 H-101 D-101 35 5 *2 3-35 H-102 D-101 206 *2 3-36 H-103 D-101 23 5 *2 3-37 H-105 D-101 39 5 *2 3-38 H-106 D-10132 6 *2 3-39 H-107 D-101 39 6 *2 3-40 H-108 D-101 25 5 *2 3-41 H-109D-101 34 5 *2 3-42 H-110 D-101 25 6 *2 3-43 H-111 D-101 17 6 *2 3-44H-112 D-101 16 5 *2 3-45 H-113 D-101 33 5 *2 3-46 H-114 D-101 32 5 *23-47 H-115 D-101 31 5 *2 3-48 H-116 D-101 27 5 *2 3-49 H-117 D-101 27 5*2 3-50 H-118 D-101 26 8 *2 3-51 H-119 D-101 32 6 *2 3-52 H-120 D-101 245 *2 *1: Comparative example *2: Present invention

The results shown in Table 5 indicate that the organic EL devices 3-4 to3-52 including the charge-transporting thin film of the presentinvention undergo a smaller variation in resistance of the luminouslayer as compared to that of the organic EL devices 3-1 to 3-3 of thecomparative examples. Accordingly, the present invention provides anorganic EL device which barely undergoes variations in physicalproperties of the thin film, i.e. luminous layer.

Example 4

Another Example will now be described. In this example, thecharge-transporting thin film is a luminous layer, and the functionalorganic compounds are a luminescent dopant and a host compound.

<<Preparation of Organic EL Full-Color Display Device>>

FIG. 17A to FIG. 17E each show a diagrammatic view illustrating astructure of an organic EL full-color display device. Indium tin oxide(ITO) with a thickness of 100 nm (transparent ITO electrodes 202) wasdeposited on a glass substrate 201 (NA 45 manufactured by NH TechnoglassCorporation) and was patterned into an anode at a pitch of 100 μm.Partitions 203 of non-photosensitive polyimide (each having a width of20 μm and a thickness of 2.0 μm) were formed on the glass substratebetween the transparent ITO electrodes by photolithography. The holeinjection layer composition containing the components listed below wasejected from an inkjet head (MJ800C, manufactured by Seiko EpsonCorporation) between the polyimide partitions on the ITO electrodes. Thesubstrate was then dried at 200° C. for 10 minutes. A hole injectionlayer 204 with a thickness of 40 nm was thereby formed. The compositionsfor blue, green, and red luminous layers as described below wereindividually ejected from the inkjet head onto the hole injection layerto form the respective luminous layers (205B, 205G, and 205R). Finally,aluminum was deposited by vacuum vapor deposition to form a cathode(206) so as to cover the luminous layers 205. The organic EL device 4-1was thereby prepared.

The organic EL device 4-2 was prepared as in the organic EL device 4-1,except that ethylene glycol monomethyl ether was replaced with2-propylene glycol monomethyl ether and 4-isopropylbiphenyl was replacedwith 4-(sec-butyl) biphenyl.

The resulting organic EL devices 4-1 and 4-2 emitted blue, green, andred light under a voltage applied to the respective electrodes, whichindicates that the organic EL devices 4-1 and 4-2 can be applied to afull-color display device.

Other organic EL devices were prepared with one of compounds D-102 toD-130, instead of compound D-101. Such organic EL devices were alsoconfirmed to be applicable to a full-color display device.

(Hole Injection Layer Composition)

Aqueous dispersion of PEDOT/PSS mixture (1.0% by mass): 20 parts by mass

Water: 65 parts by mass

Ethoxyethanol: 10 parts by mass

Ethylene glycol monomethyl ether: 5 parts by mass

(Composition for Blue Luminous Layer)

PVK: 0.7 parts by mass

Compound D-101: 0.04 parts by mass

Cyclohexylbenzene: 50 parts by mass

4-isopropylbiphenyl: 50 parts by mass

(Composition for Green Luminous Layer)

PVK: 0.7 parts by mass

D-126: 0.04 parts by mass

Cyclohexylbenzene: 50 parts by mass

4-isopropylbiphenyl: 50 parts by mass

(Composition for Red Luminous Layer)

PVK: 0.7 parts by mass

D-129: 0.04 parts by mass

Cyclohexylbenzene: 50 parts by mass

4-isopropylbiphenyl: 50 parts by mass

<<Evaluation of Organic EL Devices 4-1 and 4-2>>

The individual organic EL devices 4-1 and 4-2 thus prepared weresubjected to measurement of variations in resistance of the luminouslayer, as in Example 1. The results demonstrate that the measured valueof the resistance for the organic EL device 4-2 is less than half ofthat for the organic EL device 4-1 (the value for the organic EL device4-2 is 42 relative to that (set as 100) for the organic EL device 4-1).

These results indicate that the organic EL full-color display devicewhich is prepared with the organic EL device 4-2 containing a functionalorganic compound having chiral elements and a volatile organic materialhaving an asymmetric carbon atom and has higher stability than thatprepared with the organic EL device 4-1 which does not contain anyvolatile organic material having asymmetric carbon atom, although bothorganic EL device are included in the present invention.

Example 5

An Example will now be described. In this example, thecharge-transporting thin film is an electron transport layer, and thefunctional organic compound is an electron transport material.

<<Preparation of Organic EL Devices 5-1 to 5-15>>

The organic EL devices 5-1 to 5-15 were prepared as in the organic ELdevice 1-1, except that BCP was replaced with the compounds described inTable 6.

<<Evaluation of Organic EL Devices 5-1 to 5-15>>

These organic EL devices were each sealed as in the sealing of theorganic EL device 1-1 in Example 1 to produce a lighting device shown inFIG. 15 or FIG. 16, and the lighting device was evaluated.

The resulting samples were subjected to evaluation of a variation inresistance of the electron transport layer, as in the Example 1. Theresults are shown in Table 6.

TABLE 6 Variation in resis- Total tance of electron number of DeviceElectron transport transport layer chiral No. material (relative value)elements Remarks 5-1 BCP 100 0 *1 5-2 ET-102 72 2 *1 5-3 ET-103 68 2 *15-4 ET-101 37 4 *2 5-5 ET-102/ET-103 17 4 *2 (1/1) 5-6 ET-104 16 4 *25-7 ET-105/ET-106 31 4 *2 (1/1) 5-8 ET-107 20 4 *2 5-9 ET-108 26 5 *25-10 ET-109 34 4 *2 5-11 ET-110 22 4 *2 5-12 ET-111 28 4 *2 5-13ET-112/ET-113 19 6 *2 (1/1) 5-14 ET-114 20 4 *2 5-15 ET-115 26 6 *2 *1:Comparative example *2: Present invention

The results shown in Table 6 indicate that the organic EL devices 5-4 to5-15 including the charge-transporting thin film of the presentinvention undergo a smaller variation in resistance of the electrontransport layer as compared to that of the organic EL devices 5-1 to 5-3of the comparative examples. Accordingly, the present invention providesan organic EL device which barely undergoes variations in physicalproperties of the thin film, i.e. electron transport layer.

Example 6

An Example will now be described. In this example, thecharge-transporting thin film is a hole transport layer, and thefunctional organic compound is a hole transport material.

<<Preparation of Organic EL Devices 6-1 to 6-16>>

The organic EL Devices 6-1 to 6-16 were prepared as in the organic ELDevice 1-1, except that α-NPD was replaced with the compounds describedin Table 7.

<<Evaluation of Organic EL Devices 6-1 to 6-16>>

The resulting organic EL devices were each sealed as in the sealing ofthe organic EL device 1-1 in Example 1 to produce lighting device shownin FIG. 15 or FIG. 16, and the lighting device was evaluated.

The resulting samples were subjected to evaluation of a variation inresistance of the hole transport layer, as in the Example 1. The resultsare shown in Table 7.

TABLE 7 Variation in Total resistance of number of Device Hole transporthole transport layer chiral No. material (relative value) elementsRemarks 6-1 α-NPD 100 0 *1 6-2 HT-102 88 2 *1 6-3 HT-104 63 2 *1 6-4HT-101 25 4 *2 6-5 HT-102/HT-104 30 4 *2 (1/1) 6-6 HT-103 27 5 *2 6-7HT-105 37 5 *2 6-8 HT-106 34 4 *2 6-9 HT-107/HT-108 39 6 *2 (1/1) 6-10HT-108 12 4 *2 6-11 HT-109 36 4 *2 6-12 HT-110 10 4 *2 6-13HT-111/HT-112 20 4 *2 (1/1) 6-14 HT-113/HT-114 32 8 *2 (1/1) 6-15 HT-11529 4 *2 6-16 HT-116 18 4 *2 *1: Comparative example *2: Presentinvention

The results shown in Table 7 indicate that the organic EL devices 6-4 to6-16 including the charge-transporting thin film of the presentinvention undergo a smaller variation in resistance of the holetransport layer as compared to that of the organic EL devices 6-1 to 6-3of the comparative examples. Accordingly, the present invention providesan organic EL device which barely undergoes variations in physicalproperties of the thin film, i.e. hole transport layer.

Example 7 Preparation of Organic Photoelectric Device

An Example will now be described. In this example, thecharge-transporting thin film is a photoelectric layer, and thefunctional organic compound is selected from compounds C-101 to C-104.

<<Preparation of Organic Photoelectric Device 7-1>>

Indium tin oxide (ITO) with a thickness of 140 nm was deposited on aglass substrate to form a transparent ITO electrically conductive film,and was patterned at a pitch of 2 mm by a normal photolithographictechnique and etching with hydrochloric acid. A transparent electrodewas thereby prepared.

The patterned transparent electrode was ultrasonically cleaned in asurfactant and ultrapure water, then was ultrasonically cleaned inultrapure water, and then was dried under a nitrogen stream. Thetransparent electrode was finally cleaned in a UV-ozone environment. Anelectrically conductive polymer Baytron P4083 (available from H.C.Starck-V Tech, Ltd.) was coated onto the transparent substrate by spincoating in a thickness of 60 nm. The transparent substrate was thendried in the air at 140° C. for 10 minutes.

The substrate was then placed in a glovebox for subsequent processes ina nitrogen atmosphere. In the first stage, the substrate was heated at140° C. for 10 minutes in the nitrogen atmosphere.

A solution was prepared by dissolving 1.0 mass % PCPDTBT (polythiophenecopolymer described in Nature Mat. vol. 6 (2007) on page 497) as ap-type semiconductor material, 2.0 mass % PCBM (NANOM SPECTRA E100H,available from Frontier Carbon Corporation) as an n-type semiconductormaterial, and 2.4 mass % 1,8-octanedithiol in chlorobenzene. Thesolution was coated by spin coating at 1200 rpm for 60 seconds, whilethe solution was filtered with a filter having a pore size of 0.45 μm.The substrate was then dried at room temperature for 30 minutes. Aphotoelectric layer was thereby formed.

The substrate provided with the organic functional layers was placed ina vacuum vapor deposition system such that a shadow mask with a pitch of2 mm was perpendicular to the transparent electrode. After evacuation ofthe vacuum vapor deposition system to 10⁻³ Pa or lower, lithium fluorideand aluminum were deposited into thicknesses of 0.5 nm and 80 nm,respectively. The resulting laminate was finally heated at 120° C. for30 minutes. An organic photoelectric device 1 of the comparative examplewas thereby prepared. In each deposition process, the layer was formedat a deposition rate of 2 nm/sec and into a size of 2 mm square.

The resulting organic photoelectric device 1 was sealed with an aluminumcap and a UV-curable resin (UV RESIN XNR5570-B1, available from NagaseChemtex Corporation) in a nitrogen atmosphere. The organic photoelectricdevice 7-1 was thereby prepared.

The organic photoelectric devices 7-2 to 7-5 were prepared as in theorganic photoelectric device 7-1, except that PCBM was replaced with thecompounds described in Table 8.

<<Evaluation of Organic Photoelectric Devices 7-1 to 7-5>>

The resulting organic photoelectric devices were irradiated with lightwith an intensity of 100 mW/cm² emitted from a solar simulator (with AM1.5 G filter) for 1000 hours. The devices after the irradiation weresubjected to measurement of variations in resistance of the organicfunctional layers containing the functional organic compound of thepresent invention as in Example 1. The results shown in Table 8 indicatethat the organic photoelectric device including the charge-transportingthin film of the present invention had significantly lower values thanthe comparative example.

TABLE 8 Compound in Variation in Total number Device organic resistanceof chiral No. functional layer (relative value) elements Remarks 7-1PCBM 100 0 *1 7-2 C-101 33 4 *2 7-3 C-102 36 5 *2 7-4 C-103 17 5 *2 7-5C-104 13 5 *2 *1: Comparative example *2: Present invention

Example 8

An Example will now be described. In this example, thecharge-transporting thin film is a photosensitive layer, and thefunctional organic compound is selected from compounds C-201 to C-205.

<<Preparation of Dye-Sensitized Solar Cell>>

<<Preparation of Photoelectric Device R1>>

The photoelectric device as shown in FIG. 18 was prepared as follows.

To 375 ml of pure water, 62.5 ml of titanium tetraisopropoxide (firstgrade, available from Wako Pure Chemical Industries, Ltd.) was addeddropwise at room temperature for 10 minutes under vigorous stirring (sothat white precipitates were produced). To the resultant solution, 2.65ml of 70% aqueous nitric acid solution was added. After the reactionsystem was heated to 80° C., the mixture was continuously stirred foreight hours. The reaction mixture was concentrated under reducedpressure to a volume of approximately 200 ml, and then 125 ml of purewater and 140 g of titanium oxide powder (SUPER-TITANIA F-6, availablefrom Showa Titanium Co., Ltd.) were added to the concentrated mixture toprepare titanium oxide suspension (approximately 800 ml). The titaniumoxide suspension was applied onto a transparent electrically conductiveglass substrate coated with fluorine-doped tin oxide. The substrate wasspontaneously dried, and then was calcined at 300° C. for 60 minutes toform a titanium oxide film on the support.

A solution was then prepared by dissolving 5 g of the compound R1 in 200ml of methanol solution. The support with the titanium oxide film(semiconductor layer for photoelectric material) was immersed in theresulting solution, and 1 g of trifluoroacetic acid was added. Thesupport was then subjected to insonation for two hours. After thereaction, the titanium oxide film (semiconductor layer for photoelectricmaterial) was cleaned in chloroform, and then was dried in the vacuum. Aphotosensitive layer 302 (semiconductor for photoelectric material) wasthereby prepared.

Fluorine-doped titanium oxide was coated onto a transparent electricallyconductive glass substrate, and then platinum was coated onto thefluorine-doped titanium oxide to forma counter electrode 304. A redoxelectrolyte was prepared by dissolving tetrapropylammonium iodide andiodine in a mixed solvent of acetonitrile and ethylene carbonate at avolume ratio of 1:4, so that the tetrapropylammonium iodide and iodinewere contained at concentrations of 0.46 mol/1 and 0.06 mol/l,respectively. The redox electrolyte was injected into a space betweenthe electrically conductive support 301 and the counter electrode 304 toform a charge transfer layer 303. The photoelectric device R1 wasthereby prepared.

<<Preparation of Solar Cell 8-1>>

The sides of the photoelectric device R1 were sealed with a resin, andthe device was provided with lead. The solar cell 8-1 of the comparativeexample was thereby prepared.

The dye-sensitized solar cells 8-2 to 8-6 were prepared as in thedye-sensitized solar cell 8-1, except that the compound R1 was replacedwith the individual compounds described in Table 9.

<<Evaluation of Dye-Sensitized Solar Cells 8-1 to 8-6>>

The resulting organic photoelectric devices were irradiated with lightwith an intensity of 100 mW/cm² emitted from a solar simulator (with AM1.5 G filter) for 1000 hours. The devices after the irradiation weresubjected to measurement of variations in resistance of the organicfunctional layers containing the functional organic compound of thepresent invention as in Example 1. The results shown in Table 9 indicatethat the dye-sensitized solar cell including the charge-transportingthin film of the present invention had significantly lower values thanthat of the comparative example.

TABLE 9 Compound in Variation in Total number Solar cell organicresistance of chiral No. functional layer (relative value) elementsRemarks 8-1 R1 100 1 *1 8-2 C-201 37 4 *2 8-3 C-202 18 5 *2 8-4 C-203 314 *2 8-5 C-204 34 4 *2 8-6 C-205 23 4 *2 *1: Comparative example *2:Present invention

Example 9

An Example will now be described. In this example, thecharge-transporting thin film is a luminous layer, and the functionalorganic compound is selected from compounds F-101 to F-118.

<<Preparation of Organic EL Devices 9-1 to 9-18>>

The organic EL devices 9-1 to 9-18 were prepared as in the organic ELdevice 1-1, except that D-9 was replaced with the individual compoundsdescribed in Table 10.

<<Evaluation of Organic EL Devices 9-1 to 9-18>>

The organic EL devices were each sealed as in the sealing of the organicEL device 1-1 in Example 1 to produce lighting device shown in FIG. 15or FIG. 16, and the lighting device was analyzed.

The individual samples thus prepared were subjected to evaluation of avariation in resistance of the luminous layer, as in the Example 1. Theresults are shown in Table 10.

TABLE 10 Compound in Variation in Total number Device organic resistanceof chiral No. functional layer (relative value) elements Remarks 9-1 D-9100 1 *1 9-2 F-01 96 0 *1 9-3 F-101 72 2 *1 9-4 F-102 81 2 *1 9-5F-101/F-102 41 4 *2 (1/1) 9-6 F-103/F-104 22 4 *2 (1/1) 9-7 F-105/F-10624 5 *2 (1/1) 9-8 F-107 32 5 *2 9-9 F-108 22 4 *2 9-10 F-109 37 4 *29-11 F-110 29 4 *2 9-12 F-111/F-112 37 4 *2 (1/1) 9-13 F-113/F-114 25 8*2 (1/1) 9-14 F-114 13 4 *2 9-15 F-115 40 4 *2 9-16 F-116 46 4 *2 9-17F-117 27 4 *2 9-18 F-118 40 4 *2 *1: Comparative example *2: Presentinvention

The results shown in Table 10 indicate that the organic EL devices 9-5to 9-18 including the charge-transporting thin film of the presentinvention undergo a smaller variation in resistance of the luminouslayer as compared to that of the organic EL devices 9-1 to 9-4 of thecomparative examples. Accordingly, the present invention provides anorganic EL device which barely undergoes variations in physicalproperties of the thin film, i.e. luminous layer.

As described above, each Example demonstrates that use of an increasednumber of components without changing the energy level can reducevariations in the state of the charge-transporting thin film due todisturbance.

According to the present invention, changes in state of a chargetransfer film can be compared based on resistance as indicator of thechanges occurring in actual devices, by applying a novel nondestructivemeasurement called impedance spectroscopy. Although this is a novelmethod and the extent of errors in measured values cannot be specified,a charge-transporting thin film composed of a composition containing amixture of enantiomers and diastereomers having multiple chiral elementsaccording to the technical idea of the present invention undergoes asignificantly smaller variation in resistance than that in comparativecharge-transporting thin films. Thus, this method is believed toappropriately indicate the changes occurring in actual devices and to bevalid.

In organic EL devices and organic thin-film solar cells having acharge-transporting thin film, the short lifetime of the device is anissue which is an obstacle to practical use. In an extreme argument, thelifetime of the device entirely depends on a variation in resistance ofa charge-transporting thin film in the device. Variations in resistancecan be quantitatively evaluated from multiple correlation of variousfactors, including degradation of compounds, a change in a state ofaggregation, changes in a shape or size of crystal grains, and a changein the presence (interaction) of different molecules. Application ofimpedance spectroscopy allows nondestructive detection of a variation inresistance only for any specific film among multiple layers in an actualdevice after preparation, and is advantageous in identifying a substanceor position that causes the undesired variation, unlike in conventionalevaluation of the lifetime of the device. The present invention istherefore effective to take specific measures for improving deviceperformance.

The present invention is also significant from academic viewpoints.Compounds having chiral elements are normally applied to human, animalsand plants, and higher enantiomeric excess and diastereomeric excess arepreferred. Researchers who study on synthesis of such compounds havemade great efforts in isolation (increasing purity) of a singlecompound. Meanwhile, in the technique of the present invention,enantiomers and diastereomer do not work if they are present as a singlesubstance, and the presence of various types of isomers increases thedegree of disorder, which increases stability of a film just afterformation. Thus, the present invention is characterized by effectivenessand value entirely contrary to conventional theories in chemistry ofchiral compounds.

Various mixtures have been used in a charge-transporting thin film,particularly in a film formed by a coating process, for easy preparationof components. Unfortunately, if the components have different energylevels, charges concentrate on a material with the deepest energy level.Thus, even if the conventional methods have entropic effects as in thepresent invention, they rather cause undesired load on a specificmaterial and no significant improvement in film stability has beenactually observed.

One of the characteristics of the present invention is great easiness insynthesis of isomers from viewpoints of synthetic chemistry, in thatmany types of enantiomers and diastereomers, i.e. isomers having verysimilar physicochemical characteristics, can be synthesizedsimultaneously, without use of chiral sources which are used forincreasing enantiomeric excess or diastereomeric excess.

According to the present invention, single or combined use of compoundshaving multiple chiral elements per molecule prevents chargeconcentration and provides a fundamentally robust charge-transportingthin film, that is, increases robustness of the film againstdisturbance, such as electric current, heat, and light, based onentropic effects due to an increase in the number of components. In viewof this, the inventors have found a revolutionary technique. Theinventors also believe that the invention is an advanced technique whichsupports future development in organic electronics and which can beapplied to general use, because the technical idea of the invention canbe universally applied to any charge-transfer or electrically conductivefilm or article, in addition to the applications described herein in theExamples.

INDUSTRIAL APPLICABILITY

The charge-transporting thin film of the present invention undergoessmall variations in resistance over time during application of current.The invention further provides a charge-transporting thin film with asecondary effect of small variations over time and stable luminescentproperties. The charge-transporting thin film of the present inventioncan be suitably provided to electronic device, organicelectroluminescent elements, electrically conductive films, organicthin-film solar cells, and dye-sensitized solar cells.

EXPLANATION OF REFERENCE NUMERALS

-   1 organic semiconductor layer-   2 source electrode-   3 drain electrode-   4 gate electrode-   5 insulation layer-   6 support-   7 gate bus line-   8 source bus line-   10 organic TFT sheet-   11 organic TFTs-   12 output device-   13 storage capacitor-   14 vertical drive circuit-   15 horizontal drive circuit-   101 organic EL device-   102 glass case-   105 cathode-   106 organic EL layer-   107 glass substrate with a transparent electrode-   108 nitrogen gas-   109 water-trapping agent-   201 glass substrate-   202 ITO transparent electrode-   203 partitions-   204 hole injection layer-   205B, 205G, 205R luminous layers-   206 cathode-   301 electrically conductive support-   302 photosensitive layer-   303 charge transfer layer-   304 counter electrode-   A component A-   B component B

The invention claimed is:
 1. A charge-transporting thin film containingat least two types of functional organic compounds having chiralelements, wherein a total number of the chiral elements in each type ofthe functional organic compounds, summed over all the functional organiccompounds, is four or more, the functional organic compounds comprise ametal complex and a host compound, the metal complex has two or morechiral elements in a single molecule, thereby comprising a mixture ofenantiomers and diastereomers, and the host compound has two or morechiral elements in a single molecule, thereby comprising a mixture ofenantiomers and diastereomers.
 2. The charge-transporting thin filmaccording to claim 1, wherein the total number of the chiral elements,summed over all the functional organic compounds, is within a range offive to fifteen.
 3. The charge-transporting thin film according to claim1, further comprises at least one additional functional organic compoundwhich is not the metal complex or the host compound, wherein each of theadditional functional organic compounds comprises at least one selectedfrom a mixture of enantiomers and a mixture of diastereomers.
 4. Thecharge-transporting thin film according to claim 1, wherein at least oneof the functional organic compounds is an electron transport materialcomprising both a mixture of enantiomers and diastereomers.
 5. Thecharge-transporting thin film according to claim 1, wherein all of theat least two types of the functional organic compounds comprise both amixture of enantiomers and diastereomers.
 6. The charge-transportingthin film according to claim 1, wherein at least one of the functionalorganic compounds having chiral elements has a biaryl structure whichhas chiral elements due to hindered rotation between two aryl moieties,such that the at least one of the functional organic compounds comprisesa mixture of atropisomers.
 7. The charge-transporting thin filmaccording to claim 1, wherein at least one type of the functionalorganic compounds having chiral elements is a light-emitting compoundwhich emits light during excitation under an electric field.
 8. Thecharge-transporting thin film according to claim 7, wherein thelight-emitting compound is the metal complex.
 9. The charge-transportingthin film according to claim 1, wherein the thin film comprises avolatile organic material having a boiling point lower than 300° C.under normal pressure, wherein the volatile organic material has anasymmetric carbon atom.
 10. The charge-transporting thin film accordingto claim 1, wherein all of the functional organic compounds contained inthe charge-transporting thin film comprise a mixture of enantiomers anddiastereomers; the charge-transporting thin film contains a volatileorganic material having a boiling point lower than 300° C. under normalpressure; and the volatile organic material has an asymmetric carbonatom.
 11. The charge-transporting thin film according to claim 1,wherein the host compound is a heteroaromatic hydrocarbon derivative.12. The charge-transporting thin film according to claim 1, wherein bothof the metal complex and the host compound have a biaryl structure, havea chiral element due to hindered rotation between two aryl moieties, andcomprise a mixture of atropisomers.
 13. The charge-transporting thinfilm according to claim 11, wherein both of the metal complex and thehost compound have a biaryl structure, have a chiral element due tohindered rotation between two aryl moieties, and comprise a mixture ofatropisomers.
 14. A charge transporting thin film containing one or moretypes of functional organic compounds having chiral elements in a singlemolecule, wherein a total number of the chiral elements in each type ofthe functional organic compounds, summed over all the functional organiccompounds, is four or more, the charge-transporting thin film containsthe functional organic compounds having the chiral elements; and thethin film comprises a volatile organic material having a boiling pointlower than 300° C. under normal pressure, wherein the volatile organicmaterial has an asymmetric carbon atom.